CODEWITHSUNDEEP
javascriptecmascript-5partial-application
opengrid
opengrid

Reputation: 1944

Currying Javascript function with custom order of fixed parameters

Currying functions can be usefull:

function tag(name, value) {  
    return '<' + name + '>' + value + '</' + name + '>';
}

var strong = tag.bind(undefined, "strong");
strong("text"); // <strong>text</strong>

Now imagine we have to use another function with wrong order of parameters

function otherTag(value, name) {  
    return '<' + name + '>' + value + '</' + name + '>';
}

How to use bind function to get the same result - create strong tag using otherTag function.

How to curry this function using bind only?

I'm not interested in solution based on wrapping the otherTag function like this:

wrapOtherTag(name, value) {
    return otherTag(value, name);
}

What I want to know if it is possible to pass arguments to bind to tell the order of arguments we want to curry.

Upvotes: 1

Views: 485

Answers (2)

user663031
user663031

Reputation:

Write a function to reverse argument order:

function swap(fn) {
    return function(a, b) {
        return fn(b, a); 
    };
}

Now just call

swap(otherTag).bind(0, "strong");

Upvotes: 2

Nathan Wall
Nathan Wall

Reputation: 10674

You can write your own function to accomplish this.

// Uncurry `this` in `slice`.
var slice = Function.prototype.call.bind(Array.prototype.slice);

function curry(fn, arg, index) {
    return function curried(/* ...args */) {
        var args = slice(arguments);
        args.splice(index, 0, arg);
        return fn.apply(this, args);
    };
}

var strong = curry(tag, "strong", 0);
strong("text"); // <strong>text</strong>

var otherStrong = curry(otherTag, "strong", 1);
otherStrong("text"); // <strong>text</strong>

Upvotes: 1

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