How to write a self chain function in Javascript

Question

Right now, what I want to do is write an Array.prototype function union( array_to_union ), and I want to call it like this below:

var a = [1,2,3];
a.union([2,3,4]).union([1,3,4]) ......

and the result will be the union of those array, I wonder how can I do that?

I only know I should use Array.prototype.union = function( array_to_union){.....}.

You would just `return` the array instance in your union function. — incutonez, Jun 12 '14 at 00:26
@incutonez Thanks! But I am very new to JS, could you give me some code example? — Kuan, Jun 12 '14 at 00:27
"Put code here" questions are too broad for Stack Overflow. You need to try something first. — Anonymous, Jun 12 '14 at 00:28
Find union set(max set) among those arrays, for example [1,2,3] union [2,3,4] should [1,2,3,4] and then [1,2,3,4] union [1,3,4] is still [1,2,3,4] — Kuan, Jun 12 '14 at 00:30
I guess JavaScript currying is a technique that might work here as a pattern to follow — TGH, Jun 12 '14 at 00:30

Toothbrush · Accepted Answer · 2014-06-12T00:35:50.310

2

How about this:

Array.prototype.union = function (second) {
    return second.reduce(function (array, currentValue) {
        if (this.indexOf(currentValue) === -1) array.push(currentValue);

        return array;
    }, this).sort();
};

Test

var a = [1,2,3];
a = a.union([2,3,4]).union([1,3,4]);

Result

a = [1, 2, 3, 4]

It also sorts the array, as your examples showed in the comments.

edited Jun 12 '14 at 00:35

answered Jun 12 '14 at 00:29

Toothbrush

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@Kuan OK. I've added some code to do an union. – Toothbrush Jun 12 '14 at 00:37

score -1 · Answer 2 · answered Jun 12 '14 at 00:40

-1

Union function that can be chained together:

Array.prototype.union = function(array_to_union) {
    for (i = 0; i < array_to_union.length; i++) {
        this.push(array_to_union[i]);
    }
    return this;
}


var a = [1,2,3];              
a.union([4,5,6]).union([7,8,9]);

Note: in this case, the union function just adds 1 array onto the other (does not care about sorting or distinct values).

JS fiddle with more examples: http://jsfiddle.net/enW2Y/1/

answered Jun 12 '14 at 00:40

Lifes

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1

This is exactly what `concat()` does btw ? – adeneo Jun 12 '14 at 00:41
1

I know. The asker could just want an example of how to use Array.prototype. The question really needs clarification. – Lifes Jun 12 '14 at 00:43
@Lindsay I agree. I've marked the question as a duplicate of https://stackoverflow.com/q/3629817/3210837. – Toothbrush Jun 12 '14 at 00:44

How to write a self chain function in Javascript

2 Answers2

Test

Result