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JavaScript var – GeeksforGeeks

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3 years ago

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JavaScript var is a key phrase used to declare variables in JavaScript which are perform scoped. Earlier than the introduction of ES6 all of the key phrases in JavaScript had been declared with solely “var” key phrase. The var key phrase can be used to declare global-scope variables.

Syntax:

var variableName = valueOfVar;

Perform Scope: The variables declared inside a perform are perform scoped and can’t be accessed outdoors the perform. The variables declared with var can solely be accessed inside that perform and its enclosing perform.

The variables declared utilizing the var key phrase are hoisted on the high and are initialized earlier than the execution of code with a default worth of undefined. The variables declared within the international scope that’s outdoors any perform can’t be deleted

Instance 1: On this instance, we’ll declare a worldwide variable and entry it anyplace inside this system

Javascript

var check = 12

perform foo(){

console.log(check);

}

foo();

Output:

Instance 2: On this instance, we’ll declare a number of variables in a single assertion

Javascript

var test1 = 12,

test2= 14,

test3 = 16

perform foo(){

console.log(test1, test2, test3);

}

foo();

Output:

12 14 16

Instance 3: On this instance, we’ll see the hoisting of variables declared utilizing var

Javascript

console.log(check);

var check = 12;

Output:

undefined

Rationalization: We get the output with none error as a result of the variable check is hoisted on the high even earlier than the execution of this system started and the variable is initialized with a default worth of undefined

Instance 4: On this instance, we’ll redeclare a variable in the identical international block

Javascript

var check = 12;

var check = 100;

console.log(check);

Output:

Rationalization: We didn’t get any error when redeclaring the variable if we did the identical with the let key phrase an error can be thrown

Instance 5: On this instance, we’ll redeclare the variable in one other scope and see how it’s the authentic variable.

Javascript

var check = 12;

perform foo(){

var check = 100;

console.log(check);

}

foo();

console.log(check);

Output:

100
12

Rationalization: We didn’t get any error whereas redeclaring the variable inside one other perform scope and the unique worth of the variable is preserved.

Instance 6: On this instance, we’ll attempt to delete a worldwide variable declared utilizing va within the ‘use strict’ mode

Javascript

'use strict';

var check = 12;

delete(check);

console.log(check);

Output:

Rationalization: Each time a variable is said utilizing var in international scope it can’t be configured. Therefore it can’t be deleted utilizing the delete key phrase. and an error is thrown

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