Defining functions in a Javascript loop and using variables set in the loop

Question

I'm trying to define functions in a loop in javascript...

for (var i in myArray) {
  Object.defineProperty(object, "field"+i, { ... });
}

...and each function needs to make use of a variable which is set in that loop...

for (var i in myArray) {
  Object.defineProperty(object, "field"+i, { 
    get: function() { return "some operation" + myArray[i]; }
  });
}

...but this doesn't work because when I call the functions (long after they're defined), i evaluates to the last item in the myArray. All of the functions I defined in the loop return the same (erroneous) value.

Can anyone tell me how to accomplish my aim: make use of myArray[i] within my getter function?

Take a look at this : developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/…. — user1636522
– user1636522, Commented Apr 22, 2014 at 17:42
@procrastinator, awesome. Thank you. I used a factory function to solve the problem. — Jellicle
– Jellicle, Commented Apr 22, 2014 at 17:48
Off-topic: for..in loops are a bad way of iterating arrays. You should use ES6 for..of (currently only supported by FF), or a for(var i=0, l=myArray.length; i<l; ++i) loop. — Oriol
– Oriol, Commented Apr 22, 2014 at 18:46
Not an awesome-sounding idea. Avoid array indices, which are more powerful than array elements? Support only a single browser? How about you give some indication of why for..in loops are a 'bad' way of iterating arrays? — Jellicle
– Jellicle, Commented Apr 23, 2014 at 1:38

Jellicle · Accepted Answer · 2014-04-22 18:25:16Z

1

I created an extra closure by using a factory function:

function makeGetter(myString) {
  return function () { return "some operation" + myString; };
}
for (var i in myArray) {
  Object.defineProperty(object, "field"+i, { 
    get: makeGetter(myArray[i])
  });
}

answered Apr 22, 2014 at 18:25

Jellicle

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Comments

user3299259 · Accepted Answer · 2014-04-22 18:08:22Z

0

this could be done as following

for (var i in myArray) 
  {
  var getter=function yourName () { return "some operation" + yourName.data;}
  getter.data=myArray[i];
  Object.defineProperty(object, "field"+i, { 
  get: getter});
  }

you can define a function with

 var test=function testit () {}

testit can be use to call the function from inside the function. its a locale variable inside, its replacing arguments.callee which is depreacted in strict mode.

test is defined outside the function to call it from outside

answered Apr 22, 2014 at 18:08

user3299259

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