JavaScript Relational Operators : Relational operators are also known as comparison operators. They are used find the relationship between two values or compare relationship between two values; on comparison they yield the result true or false.
< : less than Operator > : greater than Operator
<= : less than or equal to Operator >= : greater than or equal to Operator
== : equal to Operator != : not equal to Operator
=== : strictly equal to Operator !== : strictly not equal to Operator
1. Which operator is not a relational operator ? a. < b. = c. > d. != Answer: b
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This chapter describes JavaScript's expressions and operators, including assignment, comparison, arithmetic, bitwise, logical, string, ternary and more.
At a high level, an
expression is a valid unit of code that resolves to a value. There are two types of expressions: those that have side effects (such as assigning values) and those that purely evaluate.
The expression x = 7 is an example of the first type. This expression uses the = operator to assign the value seven to the variable x. The expression itself evaluates to 7.
The expression 3 + 4 is an example of the second type. This expression uses
the + operator to add 3 and 4 together and produces a value, 7. However, if it's not eventually part of a bigger construct (for example, a variable declaration like const z = 3 + 4), its result will be immediately discarded — this is usually a programmer mistake because the evaluation doesn't produce any effects.
As the examples above also
illustrate, all complex expressions are joined by operators, such as = and +. In this section, we will introduce the following operators:
Assignment operators
Comparison
operators
Arithmetic operators
Bitwise operators
Logical operators
BigInt operators
String operators
Conditional (ternary)
operator
Comma operator
Unary operators
Relational operators
These operators join operands either formed by higher-precedence operators or one of the basic expressions. A complete and detailed list of operators and expressions is also available in the reference.
The precedence of operators
determines the order they are applied when evaluating an expression. For example:
const x =1+2*3;const y =2*3+1;
Despite * and + coming in different orders, both expressions would result in 7 because * has precedence over +, so the *-joined expression will always be evaluated first. You can override operator precedence by using parentheses (which creates a
grouped expression — the basic expression). To see a complete table of operator precedence as well as various caveats, see the Operator Precedence Reference page.
JavaScript has both binary and unary
operators, and one special ternary operator, the conditional operator. A binary operator requires two operands, one before the operator and one after the operator:
operand1 operator operand2
For example, 3 + 4 or x * y. This form is called an infix binary operator, because the operator is placed between two operands. All binary operators in JavaScript are infix.
A unary operator requires a single operand, either before or after the operator:
operator operand
operand operator
For example, x++ or
++x. The operator operand form is called a prefix unary operator, and the operand operator form is called a postfix unary operator. ++ and -- are the only postfix operators in JavaScript — all other operators, like !, typeof, etc. are prefix.
Assignment operators
An assignment operator assigns a value to its left operand based on the value of its right operand. The simple assignment operator is equal (=), which assigns the value of its right operand to its left operand. That is, x = f() is an assignment expression that assigns the value
of f() to x.
There are also compound assignment operators that are shorthand for the operations listed in the following table:
Assigning to properties
If an expression evaluates
to an object, then the left-hand side of an assignment expression may make assignments to properties of that expression. For example:
const obj ={};
obj.x =3;
console.log(obj.x);// Prints 3.
console.log(obj);// Prints { x: 3 }.const key ="y";
obj[key]=5;
console.log(obj[key]);// Prints 5.
console.log(obj);// Prints { x: 3, y: 5 }.
For more information about objects, read Working with Objects.
If an expression does not evaluate to an
object, then assignments to properties of that expression do not assign:
const val =0;
val.x =3;
console.log(val.x);// Prints undefined.
console.log(val);// Prints 0.
In strict mode, the code above throws, because one cannot assign properties to primitives.
It is an error to assign values to unmodifiable properties or to properties of an expression without properties (null or undefined).
Destructuring
For more complex assignments, the destructuring assignment syntax is a JavaScript expression that makes it possible to
extract data from arrays or objects using a syntax that mirrors the construction of array and object literals.
const foo =['one','two','three'];// without destructuringconst one = foo[0];const two = foo[1];const three = foo[2];// with destructuringconst[one, two, three]= foo;
Evaluation and nesting
In general, assignments are used within a
variable declaration (i.e., with const, let, or var) or as standalone statements).
// Declares a variable x and initializes it to the result of f().// The result of the x = f() assignment expression is discarded.let x =f();
x =g();// Reassigns the variable x to the result of g().
However, like other expressions, assignment
expressions like x = f() evaluate into a result value. Although this result value is usually not used, it can then be used by another expression.
Chaining assignments or nesting assignments in other expressions can result in surprising behavior. For this reason, some JavaScript style guides discourage chaining or nesting assignments). Nevertheless,
assignment chaining and nesting may occur sometimes, so it is important to be able to understand how they work.
By chaining or nesting an assignment expression, its result can itself be assigned to another variable. It can be logged, it can be put inside an array literal or function call, and so on.
let x;const y =(x =f());// Or equivalently: const y = x = f();
console.log(y);// Logs the return value of the assignment x = f().
console.log(x =f());// Logs the return value directly.// An assignment expression can be nested in any place// where expressions are generally allowed,// such as array literals' elements or as function calls' arguments.
console.log([0, x =f(),0]);
console.log(f(0, x =f(),0));
The evaluation result matches the expression to the right of the = sign in the "Meaning" column of the table above. That means that x = f() evaluates into
whatever f()'s result is, x += f() evaluates into the resulting sum x + f(), x **= f() evaluates into the resulting power x ** y, and so on.
In the case of logical assignments, x &&= f(), x ||= f(), and x ??= f(), the return value is that of the logical operation without the assignment, so x && f(), x || f(), and x ?? f(), respectively.
When chaining these expressions without parentheses or other grouping operators like array literals, the assignment expressions are
grouped right to left (they are right-associative), but they are evaluated left to right.
Note that, for all assignment operators other than = itself, the resulting values are always based on the operands' values before the operation.
For example, assume that the following functions f and g and the variables x
and y have been declared:
y = x = f() is equivalent to y = (x = f()), because the assignment operator = is right-associative. However, it evaluates from left to right:
The assignment expression y = x = f() starts to evaluate.
The y on
this assignment's left-hand side evaluates into a reference to the variable named y.
The assignment expression x = f() starts to evaluate.
The x on this assignment's left-hand side evaluates into a reference to the variable named x.
The function call f() prints "F!" to the console and then evaluates to the number 2.
That 2 result from f() is assigned to x.
The assignment expression
x = f() has now finished evaluating; its result is the new value of x, which is 2.
That 2 result in turn is also assigned to y.
The assignment expression y = x = f() has now finished evaluating; its result is the new value of y – which happens to be 2. x and y are assigned to 2, and the console has printed "F!".
Evaluation example 2
y = [ f(), x = g() ] also
evaluates from left to right:
The assignment expression y = [ f(), x = g() ] starts to evaluate.
The y on this assignment's left-hand evaluates into a reference to the variable named y.
The inner array literal [ f(), x = g() ] starts to evaluate.
The function call f() prints "F!" to the console and then evaluates to the number 2.
The assignment expression x = g() starts to evaluate.
The x on this assignment's left-hand side
evaluates into a reference to the variable named x.
The function call g() prints "G!" to the console and then evaluates to the number 3.
That 3 result from g() is assigned to x.
The assignment expression x = g() has now finished evaluating; its result is the new value of x, which is 3. That 3 result becomes the next element in the inner array literal (after the 2 from the f()).
The inner array literal [ f(), x = g() ] has now finished evaluating; its result is an array with two values: [ 2, 3 ].
That [ 2, 3 ] array is now assigned to y.
The assignment expression y = [ f(), x = g() ] has now finished evaluating; its result is the new value of y – which happens to be [ 2, 3 ]. x is now assigned to 3, y is now assigned to [ 2, 3 ], and the console has printed "F!" then "G!".
Evaluation
example 3
x[f()] = g() also evaluates from left to right. (This example assumes that x is already assigned to some object. For more information about objects, read Working with Objects.)
The assignment expression x[f()] = g() starts to evaluate.
The x[f()] property access on this assignment's left-hand starts to evaluate.
The x in this
property access evaluates into a reference to the variable named x.
Then the function call f() prints "F!" to the console and then evaluates to the number 2.
The x[f()] property access on this assignment has now finished evaluating; its result is a variable property reference: x[2].
Then the function call g() prints "G!" to the console and then evaluates to the number 3.
That 3 is now assigned to
x[2]. (This step will succeed only if x is assigned to an object.)
The assignment expression x[f()] = g() has now finished evaluating; its result is the new value of x[2] – which happens to be 3. x[2] is now assigned to 3, and the console has printed "F!" then "G!".
Avoid assignment chains
Chaining assignments or nesting assignments in other expressions can result in surprising behavior. For this reason,
chaining assignments in the same statement is discouraged).
In particular, putting a variable chain in a const, let, or var statement often does not work. Only the outermost/leftmost variable would get declared; other variables within the assignment chain are not declared by the const/let/var statement. For example:
This statement seemingly declares the variables x, y, and z. However, it only actually declares the variable z. y
and x are either invalid references to nonexistent variables (in strict mode) or, worse, would implicitly create global variables for x and y in sloppy mode.
Comparison operators
A comparison operator compares its operands and returns a logical value based on whether the comparison is true. The operands can be numerical, string, logical, or
object values. Strings are compared based on standard lexicographical ordering, using Unicode values. In most cases, if the two operands are not of the same type, JavaScript attempts to convert them to an appropriate type for the comparison. This behavior generally results in comparing the operands numerically. The sole exceptions to type conversion within comparisons involve the
=== and !== operators, which perform strict equality and inequality comparisons. These operators do not attempt to convert the operands to compatible types before checking equality. The following table describes the comparison operators in terms of this sample code:
const var1 =3;const var2 =4;
Note:=> is not a comparison operator but rather is the notation for
Arrow functions.
Arithmetic operators
An arithmetic operator takes numerical values
(either literals or variables) as their operands and returns a single numerical value. The standard arithmetic operators are addition (+), subtraction (-), multiplication (*), and division (/). These operators work as they do in most other programming languages when used with floating point numbers (in particular, note that division by zero produces
Infinity). For example:
1/2;// 0.51/2===1.0/2.0;// this is true
In addition to the standard arithmetic operations (+, -, *, /), JavaScript provides the arithmetic operators listed in the following table:
Bitwise operators
A bitwise operator treats their operands as a set of 32 bits (zeros and ones), rather than as decimal, hexadecimal, or octal numbers. For example, the decimal number nine has a binary representation of 1001. Bitwise operators perform their operations on such binary representations, but they
return standard JavaScript numerical values.
The following table summarizes JavaScript's bitwise operators.
Bitwise logical operators
Conceptually, the bitwise logical operators work
as follows:
The operands are converted to thirty-two-bit integers and expressed by a series of bits (zeros and ones). Numbers with more than 32 bits get their most significant bits discarded. For example, the following integer with more than 32 bits will be converted to a 32-bit integer:
Each bit in the first operand is paired with the corresponding bit in the second operand: first bit to first bit, second bit to second bit, and so on.
The operator is applied
to each pair of bits, and the result is constructed bitwise.
For example, the binary representation of nine is 1001, and the binary representation of fifteen is 1111. So, when the bitwise operators are applied to these values, the results are as follows:
Note that all 32 bits are inverted using the Bitwise NOT operator, and that values with the most significant (left-most) bit set to 1 represent negative numbers (two's-complement representation). ~x evaluates to the
same value that -x - 1 evaluates to.
Bitwise shift operators
The bitwise shift operators take two operands: the first is a quantity to be shifted, and the second specifies the number of bit
positions by which the first operand is to be shifted. The direction of the shift operation is controlled by the operator used.
Shift operators convert their operands to thirty-two-bit integers and return a result of either type Number or BigInt:
specifically, if the type of the left operand is BigInt, they return BigInt; otherwise, they return Number.
The shift operators are
listed in the following table.
Logical operators
Logical operators are typically used with Boolean (logical) values; when they are, they return a Boolean value. However, the && and || operators actually return
the value of one of the specified operands, so if these operators are used with non-Boolean values, they may return a non-Boolean value. The logical operators are described in the following table.
Examples of expressions that can be converted to false are those that evaluate to null, 0, NaN, the empty string (""), or undefined.
The following code shows examples of the && (logical AND) operator.
const a1 =true&&true;// t && t returns trueconst a2 =true&&false;// t && f returns falseconst a3 =false&&true;// f && t returns falseconst a4 =false&&(3===4);// f && f returns falseconst a5 ='Cat'&&'Dog';// t && t returns Dogconst a6 =false&&'Cat';// f && t returns falseconst a7 ='Cat'&&false;// t && f returns false
The following code shows examples of the || (logical
OR) operator.
const o1 =true||true;// t || t returns trueconst o2 =false||true;// f || t returns trueconst o3 =true||false;// t || f returns trueconst o4 =false||(3===4);// f || f returns falseconst o5 ='Cat'||'Dog';// t || t returns Catconst o6 =false||'Cat';// f || t returns Catconst o7 ='Cat'||false;// t || f returns Cat
The following code shows examples of the ! (logical NOT) operator.
As logical expressions are evaluated left to
right, they are tested for possible "short-circuit" evaluation using the following rules:
false && anything is short-circuit evaluated to false.
true || anything is short-circuit evaluated to true.
The rules of logic guarantee that these evaluations are always correct. Note that the anything part of the above expressions is not evaluated, so any side effects of doing so do not take effect.
Note that for the second case, in modern code you can use the
Nullish coalescing operator (??) that works like ||, but it only returns the second expression, when the first one is "nullish", i.e. null or
undefined. It is thus the better alternative to provide defaults, when values like '' or 0 are valid values for the first expression, too.
BigInt operators
Most operators that can be used between numbers can be used between BigInt values as well.
// BigInt additionconst a =1n+2n;// 3n// Division with BigInts round towards zeroconst b =1n/2n;// 0n// Bitwise operations with BigInts do not truncate either sideconst c =40000000000000000n>>2n;// 10000000000000000n
One exception is
unsigned right shift (>>>), which is not defined for BigInt values. This is because a BigInt does not have a fixed width, so technically it does not have a "highest bit".
const d =8n>>>2n;// TypeError: BigInts have no unsigned right shift, use >> instead
BigInts and numbers are not mutually replaceable — you cannot mix them in calculations.
const a =1n+2;// TypeError: Cannot mix BigInt and other types
This is because BigInt is neither a subset nor a superset of
numbers. BigInts have higher precision than numbers when representing large integers, but cannot represent decimals, so implicit conversion on either side might lose precision. Use explicit conversion to signal whether you wish the operation to be a number operation or a BigInt one.
const a =Number(1n)+2;// 3const b =1n+BigInt(2);// 3n
You can compare BigInts with numbers.
const a =1n>2;// falseconst b =3>2n;// true
String operators
In addition to the comparison operators, which can be used on string values, the concatenation operator (+) concatenates two string values together, returning another string that is the union of the two operand strings.
For example,
console.log('my '+'string');// console logs the string "my string".
The shorthand assignment operator
+= can also be used to concatenate strings.
For example,
let mystring ='alpha';
mystring +='bet';// evaluates to "alphabet" and assigns this value to mystring.
Conditional (ternary) operator
The
conditional operator is the only JavaScript operator that takes three operands. The operator can have one of two values based on a condition. The syntax is:
If condition is true, the operator has the value of val1. Otherwise it has the value of val2. You can use the conditional operator anywhere you would use a standard operator.
For example,
const status = age >=18?'adult':'minor';
This statement assigns the value "adult" to the variable status if age is eighteen or more. Otherwise, it assigns the value "minor" to status.
Comma operator
The
comma operator (,) evaluates both of its operands and returns the value of the last operand. This operator is primarily used inside a for loop, to allow multiple variables to be updated each time through the loop. It is regarded bad style to use it elsewhere, when it is not necessary. Often two separate statements can and should be used instead.
For
example, if a is a 2-dimensional array with 10 elements on a side, the following code uses the comma operator to update two variables at once. The code prints the values of the diagonal elements in the array:
const x =[0,1,2,3,4,5,6,7,8,9];const a =[x, x, x, x, x];for(let i =0, j =9; i <= j; i++, j--){// ^
console.log(`a[${i}][${j}]= ${a[i][j]}`);}
Unary
operators
A unary operation is an operation with only one operand.
delete
The delete operator deletes an object's property. The syntax is:
where object is the name of an object, property is an existing property, and propertyKey is a string or symbol referring to an existing property.
If the delete operator succeeds, it removes the property from the object. Trying to access it afterwards will yield undefined. The delete operator returns true if the operation is possible; it returns false if the operation is not possible.
Since arrays are just objects, it's technically possible to delete elements from them. This is however regarded as a bad practice, try to avoid it. When you delete an array property, the array length is not affected and other elements are not re-indexed. To achieve that behavior, it is much better to just overwrite the element with the value undefined. To actually manipulate the array, use the various array methods such as
splice.
typeof
The typeof
operator is used in either of the following ways:
The typeof operator returns a string indicating the type of the unevaluated operand. operand is the string, variable, keyword, or object for which the type is to be returned. The parentheses are optional.
The void operator is used in either of the following ways:
void(expression)void expression
The void operator specifies an expression to be evaluated without returning a value.
expression is a JavaScript expression to evaluate. The parentheses surrounding the expression are optional, but it is good style to use them.
Relational operators
A relational operator compares its operands and
returns a Boolean value based on whether the comparison is true.
in
The in operator returns true if the specified property is in the specified object. The syntax is:
propNameOrNumber in objectName
where propNameOrNumber is a string, numeric, or symbol expression representing a property name or array index, and objectName is the name of an object.
The following examples show some uses of the in operator.
// Arraysconst trees =['redwood','bay','cedar','oak','maple'];0in trees;// returns true3in trees;// returns true6in trees;// returns false'bay'in trees;// returns false (you must specify the index number,// not the value at that index)'length'in trees;// returns true (length is an Array property)// built-in objects'PI'in Math;// returns trueconst myString =newString('coral');'length'in myString;// returns true// Custom objectsconst mycar ={make:'Honda',model:'Accord',year:1998};'make'in mycar;// returns true'model'in mycar;// returns true
instanceof
The instanceof operator returns true if the specified object is of the specified object type. The syntax is:
objectName instanceofobjectType
where objectName is the name of the object to compare to objectType, and objectType is an object type, such as Date or
Array.
Use instanceof when you need to confirm the type of an object at runtime. For example, when catching exceptions, you can branch to different exception-handling code depending on the type of exception thrown.
For example, the following code uses instanceof to determine whether theDay is a Date object. Because theDay is a Date object, the statements
in the if statement execute.
const theDay =newDate(1995,12,17);if(theDay instanceofDate){// statements to execute}
Basic expressions
All operators eventually operate on one or more basic expressions. These basic expressions include
identifiers and literals, but there are a few other kinds as well. They are briefly introduced below, and their semantics are described in detail in their respective reference sections.
this
Use the this keyword to refer to the current object. In general, this refers to the calling object in a method. Use this either with the dot or the bracket notation:
this['propertyName']this.propertyName
Suppose a function
called validate validates an object's value property, given the object and the high and low values:
You could call validate in each form element's onChange event handler, using this to pass it to the form element, as in the following example:
<p>Enter a number between 18 and 99:</p><inputtype="text"name="age"size="3"onChange="validate(this,18,99);"/>
Grouping operator
The grouping operator ( ) controls the precedence of evaluation in expressions. For example, you can override multiplication and division first, then addition and subtraction to evaluate addition first.
const a =1;const b =2;const c =3;// default precedence
a + b * c // 7// evaluated by default like this
a +(b * c)// 7// now overriding precedence// addition before multiplication(a + b)* c // 9// which is equivalent to
a * c + b * c // 9
new
You can use the new operator to create an instance of a user-defined object type or of one of the built-in object types. Use new as follows:
The super keyword is used to call functions on an object's parent. It is useful with classes to call
the parent constructor, for example.
super([arguments]);// calls the parent constructor.super.functionOnParent([arguments]);
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What are relational operators examples?
Relational Operators.
What are the operators in JavaScript with example?
JavaScript Arithmetic Operators.
What are the 6 types of relational operators?
Types of Relational Operators in C.
Equal to..
Not equal to..
Less than..
Greater than..
Less than or equal to..
Greater than or equal to..
What are the 4 types of JavaScript operators?
JavaScript includes operators that perform some operation on single or multiple operands (data value) and produce a result. JavaScript includes various categories of operators: Arithmetic operators, Comparison operators, Logical operators, Assignment operators, Conditional operators.