Question

Help me please solve my problem. I’m using underscore.js lib and I have a snippet that demonstrates what problem I have:

var a = [4, 3, 2, 1];
var b = _(a).select(function(el){ return el>1; }).push(6);
console.log("b: "+b);
// b: 4
var c = _(a).select(function(el){ return el>1; });
c.push(6);
console.log("c: "+c);
// c: [4, 3, 2, 6]

What is going on? Why select() function returns something strange – like an object with integer keys. But when we put results of select() we can use array native methods again. Why? What is it?
I know that we can use native array methods inside of chain(), but snippet results is really strange…

Answer 1

That is because the push method returns the index at which the value was inserted into the array.
For more details see the push method documentation
The b variable is the same as:

var c = _(a).select(function(el){ return el>1; });
c = c.push(6);
console.log("c: "+c);
// c: 4