How to initialize a javascript array with its own elements and elements of another array?

Question

Here's a sample code that resembles my situation:

var customProcessor = function test1(arga, argb, argc, argd) {
  console.log('customProcessor', 'arga', arga);
  console.log('customProcessor', 'argb', argb);
  console.log('customProcessor', 'argc', argc);
  console.log('customProcessor', 'argd', argd);
};

var utilityMethod = function test2(arga, argb, someFunc, cbArgs) {
  console.log('utilityMethod', 'arga', arga);
  console.log('utilityMethod', 'argb', argb);
  cbArgs.unshift(argb);
  cbArgs.unshift(arga);
  someFunc.apply(this, cbArgs); // INTENT: someFunc(arga, argb, argc, argd);
};

utilityMethod('argA', 'argB', customProcessor, ['argC','argD']);

The code above manages to pass all 4 required arguments to my customProcessor method but the following lines aren't the most readable in terms of intent:

  cbArgs.unshift(argb);
  cbArgs.unshift(arga);
  someFunc.apply(this, cbArgs); // INTENT: someFunc(arga, argb, argc, argd);

Is there some way to write them in a more self-explanatory fashion ... using a JS syntax that I might not know about?

Here's what I'm imagining would be more readable:

  // not real code
  someFunc.apply(this, [arga, argb, cbArgs]);

but I need to know if there is a realistic JS syntax for accomplishing this?

@ASDFGerte - thanks! would you mind answering so i can mark it as the correct answer? — pulkitsinghal
– pulkitsinghal, Commented Aug 19, 2017 at 1:51

ASDFGerte · Accepted Answer · 2017-08-19 01:57:57Z

2

Use the spread syntax:

[arga, argb, ...cbArgs]

Note that this also works directly on the function call, replacing apply (if you do not need an explicit this), e.g. someFunc(arga, argb, ...cbArgs)

edited Aug 19, 2017 at 1:57

answered Aug 19, 2017 at 1:51

ASDFGerte

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2 Comments

pulkitsinghal Over a year ago

yes you are right again! both work: someFunc.apply(this, [arga, argb, ...cbArgs]); or someFunc(arga, argb, ...cbArgs);

Slai Over a year ago

@pulkitsinghal make sure to check both tabs in the browser support section as it's not supported in IE and some older bowsers developer.mozilla.org/en/docs/Web/JavaScript/Reference/…

Slai · Accepted Answer · 2017-08-19 03:13:09Z

1

function customProcessor(a, b, c, d) {
  console.log('customProcessor:', a, b, c, d);
};

function utilityMethod(arga, argb, someFunc, cbArgs) {
  console.log('utilityMethod  :', arga, argb);
  someFunc(arga, argb, cbArgs[0], cbArgs[1]); 
  // or
  someFunc.apply(this, [arga, argb].concat(cbArgs)); 
};

utilityMethod('argA', 'argB', customProcessor, ['argC','argD']);

edited Aug 19, 2017 at 3:13

answered Aug 19, 2017 at 2:50

Slai

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