is this a closure in JavaScript as Im not sure?

Question

Is this a closure in JavaScript?

var test = function(b){
    var a = 1;
    return function(b){
        a + b
    }
};
var c = test(2);

Please see http://stackoverflow.com/questions/111102/how-do-javascript-closures-work — topcat3, Feb 28 '13 at 14:42
Yes, the returned function is a closure. It's kind-of strange, because the parameter to the "test" function isn't used. — Pointy, Feb 28 '13 at 14:42
As @Pointy mentioned, this will **not** return `3`. This will return the anonymous function `function(b) { a + b }` (which doesn't actually do anything, as it doesn't return anything). — h2ooooooo, Feb 28 '13 at 14:44

score 2 · Accepted Answer · answered Feb 28 '13 at 14:48

A closure is introduced then you define a function within test that returns local properties of the test function. an example of a closure would be here:

;(function() {

    var local = 123

    window.foo = function() {
        return local
    }
})()

What you're pretty close to in your example is currying, which involves a function that returns a function to take a second parameter. e.g:

function add(a) {
    return function(b) {
        return a + b;
    }
}

add(5)(6) // 11

score 0 · Answer 2 · edited May 23 '17 at 12:21

var a; and parameter b of the outer function are part of the closure of the inner function. For detailed explanation of closures have a look in the FAQ

var test = function(b){ // <= param b is part of the closure of the inner function
    var a = 1;          // <= a is part of the closure of the inner function as well 
    return function(b){ // <= the inner function
        a + b           // <= here you are just add ind a and b together
                        //    return a + b; //would be more appropriate
    }
};
var c = test(2);

Avinash Maurya · Answer 3 · 2018-09-12T03:04:19.560

0

var globalVar = "xyz";

(function outerFunc(outerArg) {
    var outerVar = 'a';
    
    (function innerFunc(innerArg) {
    var innerVar = 'b';
    
    console.log(
        "outerArg = " + outerArg + "\n" +
        "innerArg = " + innerArg + "\n" +
        "outerVar = " + outerVar + "\n" +
        "innerVar = " + innerVar + "\n" +
        "globalVar = " + globalVar);
    
    })(456);
})(123);

this code is same to above code but is new way of writing result and output will be same })(123); here firstly automatically call outer function pass argument 123 then })(456); call inner function automatically

Note in this way no return require

edited Sep 12 '18 at 03:04

answered Sep 12 '18 at 02:47

Avinash Maurya

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4

Whenever we use function inside another function, a closure is used. means A closure is basically when an inner function has access to variables outside of its scope – Avinash Maurya Sep 12 '18 at 02:49

Avinash Maurya · Answer 4 · 2018-09-12T02:59:15.133

var globalVar = "xyz";

function outerFunc(outerArg) {
    var outerVar = 'a';
    
     var r3= function innerFunc(innerArg) {
    var innerVar = 'b';
    
    console.log(
        "outerArg = " + outerArg + "\n" +
        "innerArg = " + innerArg + "\n" +
        "outerVar = " + outerVar + "\n" +
        "innerVar = " + innerVar + "\n" +
        "globalVar = " + globalVar);
    
    };
 return r3;
};

var r=outerFunc(123);
r(456);

var r=outerFunc(123); ...here we have called outer-function and assign this result return in r variable we cannot use inner function directly. we have to call outer function and assign their return in varible because above code return function

above code we can also write this simple way old format we have use inner and outer function inner function we have pass in a variable var r3 which is call when out-function call then as return of outer function is inner function — Avinash Maurya, Sep 12 '18 at 02:52

is this a closure in JavaScript as Im not sure?

4 Answers4