js pass additional argument to function

Question

I have the following code:

    var createThumb128 = function(fileObj, readStream, writeStream) {
        gm(readStream, fileObj.name()).resize('128', '128').stream().pipe(writeStream);
    };

    var store = new FS.Store.GridFS("thumbs_128", { transformWrite: createThumb128})

How can I replace the hardcoded 128 size strings with arguments that I pass to the createThumb function?

I assume that I cannot just add the additional parameter since the transformWrite property requires a function with the specific 3 parameter signature.

Tong Shen · Accepted Answer · 2015-12-22 19:20:22Z

2

You can try "Currying" https://en.wikipedia.org/wiki/Currying

var createThumb = function(size) {
    return function(fileObj, readStream, writeStream) {
        gm(readStream, fileObj.name()).resize(size, size).stream().pipe(writeStream);
    };
}

var store = new FS.Store.GridFS("thumbs_128", { transformWrite: createThumb('128')})

answered Dec 22, 2015 at 19:20

Tong Shen

1,3669 silver badges18 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Jared Smith Over a year ago

This is a good answer in terms of code, but doesn't curry the actual function.

lex82 Over a year ago

Right, currying would turn a 4 param function into several smaller functions. Here you just produce functions with createThumb. It solves the problem, but it's not currying.

lex82 · Accepted Answer · 2015-12-22 19:28:13Z

2

If transformWrite expects the given three parameters, you have to supply a respective function. However, you can just create such a function with the size parameters you want.

What you need is a function that creates another function:

var makeCreateThumb = function(param) {
    return function(fileObj, readStream, writeStream) {
        gm(readStream, fileObj.name())
            .resize(param, param)
            .stream()
            .pipe(writeStream);
    };
}

Use it like this:

var store = new FS.Store.GridFS("thumbs_128", { 
    transformWrite: makeCreateThumb('128')
})

edited Dec 22, 2015 at 19:28

answered Dec 22, 2015 at 19:21

lex82

11.4k2 gold badges48 silver badges72 bronze badges

1 Comment

Jared Smith Over a year ago

Bonus upvote for improving the formatting of the original code.

epascarello · Accepted Answer · 2015-12-22 19:26:56Z

0

First option is to return a function.

function abc (_custom) {
  return function (a, b, c) {
      console.log(arguments, _custom);
  }
}

var x = abc();
console.log(x(1,2,3));

Another option is to use bind

function abc (_custom, a,b,c) {
  console.log(arguments);
}

var x = abc.bind(this, 128);
x(1,2,3)

answered Dec 22, 2015 at 19:26

epascarello

208k20 gold badges206 silver badges246 bronze badges

Comments

JNF · Accepted Answer · 2015-12-22 19:36:57Z

0

Use currying, as suggested by @TongShen - with bind.

bind allows you to take a function with n arguments, with bind you can receive a function of n-x where you can fix the first n.

For your case, make it a 4 argument function:

 var createThumb128 = function(len, fileObj, readStream, writeStream) {
        gm(readStream, fileObj.name()).resize(len, len).stream().pipe(writeStream);
    };

then create a 3 argument copy, fixing the '128' length, and send that:

var lengthFixed128 = createThumb128 .bind(undefined, '128'); //first argument binds to a context, can be left undefined for our purpose

var store = new FS.Store.GridFS("thumbs_128", { transformWrite: lengthFixed128 })

edited Dec 22, 2015 at 19:36

answered Dec 22, 2015 at 19:25

JNF

3,7403 gold badges35 silver badges65 bronze badges

Collectives™ on Stack Overflow

js pass additional argument to function

4 Answers 4

2 Comments

1 Comment

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

2 Comments

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related