CODEWITHSUNDEEP
javascriptfunctionvariablesscope
sonaxaton
sonaxaton

Reputation: 49

javascript copy a variable for use in function

I'm not really sure how to word this question better, but basically my problem is this:

I have code like this (not exactly, this code is really simple and mine is a little more complicated):

var funcs = [];
for (var i = 0; i < 10; i++) {
    funcs[i] = function() { return i; };
}

So the idea is that each function in funcs will return each number from 0 to 9 when called. But the problem is that each one is still referring to the variable i when called, so they will all return 9. How do I get this work as intended (i.e. for all n, funcs[n]() === n)? How do I get each function scope to capture only the current value of i, not the value that changes?

Upvotes: 1

Views: 151

Answers (2)

ZEE
ZEE

Reputation: 5859

i could do like so :

var funcs = [];
for (var i = 0; i < 10; i++) {
    (function (i) {
        funcs[i] = function () {
            return i;
        };
    })(i);
}
alert(funcs[3]());

creating a separate activation frame for each iteration

you can alternatively use map:

var numbers = [];
for (var i = 0; i < 10; i++) {
    numbers.push(i);
}

var funcs = numbers.map(function (i) {
    return function () { return i; };
});
alert(funcs[3]());

Upvotes: 2

radiaph
radiaph

Reputation: 4091

var funcs = [];
for (var i = 0; i < 10; i++) {
    funcs[i] = makeFunction(i);
}

function makeFunction(i) {
    return function() {
        return i;
    }
}

i in the returned function is bound to the local variable i in makeFunction rather than i in your main block of code.

Upvotes: 0

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