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Why can't I click inside an array and use it in a function argument in javascript?

Why are b and c not identical in the below code? What is the order of execution of the statement on line # 2?

var a = [1,2];
var b = new Array(a.push(1)); //[undefined, undefined, undefined]
var c = new Array(a);         // [[1, 2, 1]]
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2 answers


The function .push()

returns the new length of the array, not the array itself. Thus, it is b

initialized to an empty array of 3 elements, because it .push()

returns 3 (after being added 1

to the end of the array a

).



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You can also clone an array using a function slice

as an alternative to constructors. And use this path if you want it to a

remain unchanged.



var a = [1,2];
var b = a.slice(); 
b.push(1);            // [[1, 2, 1]]
var c = b.slice();    // [[1, 2, 1]]
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