I'm confused with the output.
var arrLike = {0:'Martin', 1:78, 2:67, 3:['L', 'M', 'P'], length: 4};
If I use slice() on arrLike:
var newArr = Array.prototype.slice.call(arrLike, 0);
Output:
console.log(newArr);
["Martin", 78, 67, Array[3]]
How does this happen? I can't wrap up my head around with the output.
Preface: Note that the Array[3] in your console output is just how the console is showing it to you. Your newArr is really:
["Martin", 78, 67, ['L', 'M', 'P']]
It happens because that's how slice is defined. Loosely speaking it:
length property of what you give it0) to the ending index (default length - 1); call the loop variable k
k into the array at index k - start.length of the returned array to k - start.Or (again very loosely):
function slice(start, end) {
var n, k, result;
start = arguments.length < 1 ? 0 : +start;
end = arguments.length < 2 ? +this.length : +end;
result = [];
for (var k = start, n = 0; k < end; ++k, ++n) {
if (n in this) {
result[n] = this[k];
}
}
result.length = n;
return result;
}
Since your arrLike object has a length property and has properties with the names 0, 1, 2, and 3, you get the result you've shown.
Check out the spec for slice(). The slice() function will default the end parameter, which you did not specify, to this.length, and...
- If end is undefined, let relativeEnd be len; else let relativeEnd be ToInteger(end).
Therefore, you're only pushing the first 4 non-element properties of the arrLike object into the new array.
Try using...
var arrLike = {0:'Martin', 1:78, 2:67, 3:['L', 'M', 'P'], length: 6, 4: 'test'};
length) isn't an "element," it's a non-element property ("element" being the term we [and the spec] use for properties that have a name that fits the definition of an "array index").