Javascript - Why returning array.push(x) from a fu

问题:

I'd like to know why the following function works:

function foo(list){
    var array = [];
    array.push(list);
    return array;
}

> foo([1,2,3])
[[1,2,3]]

while this one doesn't:

function foo(list){
    var  array = [];
    return array.push(list);
}

> foo([1,2,3])
1 

What's the difference between them?

回答1:

If you look at the definition of the push method, it returns the length of the array after the push, not the array itself, that is why it is returning 1.

The push() method adds one or more elements to the end of an array and returns the new length of the array.

You are pushing an array with 3 elements to the new array, so in the new array you have an array as its content thus 1 is returned