JavaScript: why can't I chain Array.prototype.filter with .push()?
arrays, chaining, filtering, javascript, method-chaining
Solution
The problem is not with what `filter()` returns, instead it is with what `push()` returns.
`push()` returns the new length of the array, and not the array itself.
So when you do:
var arr2 = arr.filter(function(elmnt) { return elmnt.indexOf("a") > -1; }).push("aaa");
`arr2` will be assigned the new length of the array (which happens to be 4 in your case), and not the new array as such.
A modified version that'll do what you want would be:
var arr = ["a", "ab", "c", "ad"], arr2;
(arr2 = arr.filter(function(elmnt) { return elmnt.indexOf("a") > -1; })).push("aaa");
// now arr2 is ["a", "ab", "ad", "aaa"]
Problem
If `Array.prototype.filter` returns an array, why can't I invoke `push()` on this return value immediately? Example: ``` var arr = ["a", "ab", "c", "ad"]; var arr2 = arr.filter(function(elmnt) { return elmnt.indexOf("a") > -1; }); // result: ["a", "ab", "ad"] arr2.push("aaa"); // result: ["a", "ab", "ad", "aaa"] ``` Ok so far. But what about chaining that `push()` call to the `filter()` call? ``` var arr = ["a", "ab", "c", "ad"]; var arr2 = arr.filter(function(elmnt) { return elmnt.indexOf("a") > -1; }).push("aaa"); // result: 4 ``` Why does chaining `filter()` and `push()` result in the number of elements that I would expect, rather than an array of those elements?