In Javascript, what is a sure way to loop through an array of 3 strings?

Question

Something like this works, but looks a bit clumsy:

for (i in {foo: 1, bar: 1, wah: 1}) {  // loops through foo, bar, wah
  console.log(i + " haha");            // can view using Firebug or Chrome 
}

if using an array, I don't want to create any global temporary variable for the array... Also, this has to work in any modern browser IE7 / FF / Chrome / Safari. thanks.

Answer 1

You need to declare i for certain browsers.

I would use the initialization section of a for loop to declare the variables.

Array:

for (var i = 0, arr = ['foo', 'bar', 'wah']; i < arr.length; i++) {
  console.log(arr[i] + " haha");
}

Answer 2

If the requirement is that you don't want to create a variable in the global (or current) scope, but just want to use the Array literal, then use forEach, though you'll need to prototype it into browsers that don't support it.

["foo", "bar", "wah"].forEach(function( v, i, arr ){
  console.log(i + ' ' + v + " haha");
});

Here's MDC's implementation of a forEach to prototype into Array.

if (!Array.prototype.forEach)
{
  Array.prototype.forEach = function(fun /*, thisp */)
  {
    "use strict";

    if (this === void 0 || this === null)
      throw new TypeError();

    var t = Object(this);
    var len = t.length >>> 0;
    if (typeof fun !== "function")
      throw new TypeError();

    var thisp = arguments[1];
    for (var i = 0; i < len; i++)
    {
      if (i in t)
        fun.call(thisp, t[i], i, t);
    }
  };
}

Answer 3

Okay I'm posting this cause I like strange code, so go easy on me...

If you absolutely do not want to create a temporary variable, global or local, and cannot use or add the forEach function (as in patrick dw's answer), you can drag out the dreaded with statement to do the job. It's not exactly pretty...

with(['foo', 'bar', 'wah'])
  while(valueOf().length)
    console.log(valueOf().shift())

Look ma, no variables!

If you are okay with using lexically scoped variables, then you can do things a bit cleaner...

with({a: ['foo', 'bar', 'wah']})
  while(a.length)
    console.log(a.shift())

You could do the same thing with a self-executing anonymous function, but with horrid syntax and (likely) lesser performance.

Regardless, I strongly recommend you use forEach if you can, or just...you know, local variables.

Answer 4

I think that will look better:

   function show(arr){
     for(el in arr){
      console.log(arr[el])   
     }    
    }
    show({foo: 1, bar: 1, wah: 1});

Answer 5

Why not use the var keyword to denote a local variable (as variables declared without the var keyword are automatically global).

Also { ... } denotes a JavaScript object, not an array. You can define arrays with [ ... ]:

var myArray = ["one", "two", "three"];

for (var i in myArray) {
    console.log(myArray[i] + " haha");
}

Hope that helps!

Answer 6

You want to be careful when using for in as you may get keys that are in the prototype chain and not actually part of the object. So in your example you'd want to use:

var obj = {foo: 1, bar: 1, baz: 1};
for(var key in obj) {
   if(obj.hasOwnProperty(key)) {
       console.log(key, obj[key]); //key, value
   }
}

Answer 7

How about

javascript:
Array.prototype.enum = function (fn) {
  for( var i=0; i < this.length; i++ )
    fn( this[i] )
};

["one","two","tri"].enum( function(item){
  alert(item)
})

reformatted