Question

erase: function(item){
        for (var i = this.length; i--;) {
            if (this[i] === item) this.splice(i, 1);
        }
        return this;
    }

How would this (var i = this.length; i--;) syntactic construct work?

Should there be three sections? What is it in this case?

from here.

Answer 1

It initializes i to this.length, and uses the condition check to also decrement it. When it gets to zero, which is a falsy value, the loop stops.

But note that because you decrement in the check, the loop starts at this.length - 1 and ends at 0. So it’s equivalent to:

(var i = this.length - 1; i >= 0; i--)

But please refrain from using this kind of syntax, as its behavior is confusing – as you might have noticed.