JavaScript - get array element fulfilling a condition

I'm learning JavaScript using W3C and I didn't find an answer to this question.

I'm trying to make some manipulations on array elements which fulfill some condition.

Is there a way to do it other than running on the array elements in for loop? Maybe something like (in other languages):

foreach (object t in tArray)
   if (t follows some condition...) t++;

another thing, sometimes I want to use the element's value and sometimes I want to use it as a reference. what is the syntactical difference?

As well, I'll be happy for recommendations on more extensive sites to learn JavaScript from. thanks

Solution 1:

In most browsers (not IE <= 8) arrays have a filter method, which doesn't do quite what you want but does create you an array of elements of the original array that satisfy a certain condition:

function isGreaterThanFive(x) {
     return x > 5;
}

[1, 10, 4, 6].filter(isGreaterThanFive); // Returns [10, 6]

Mozilla Developer Network has a lot of good JavaScript resources.

Solution 2:

Use ES6 Array.filter() and arrow functions with expression body:

myArray.filter(x => x > 5)

A bit more concise than @Beauty's answer.

Solution 3:

Here a short way to write a filter. From an array of numbers it returns all values greater than 5.

myArray.filter((x) => { return x > 5; })

Usage example:

var filterResult = [1, 10, 4, 6].filter((x) => { return x > 5; });
console.log(filterResult); // returns [ 10, 6 ]

And here a filter for an array of objects, which checks a property condition.

myArray.filter((x) => { return x.myNumber > 5; })

Usage example:

var myArray = [{myNumber: 1, name: 'one'}, {myNumber: 3, name: 'tree'}, {myNumber: 6, name: 'six'}, {myNumber: 8, name: 'eight'}];
var result = myArray.filter((x) => { return x.myNumber > 5; });
console.log(result); // returns [ { myNumber: 6, name: 'six' }, { myNumber: 8, name: 'eight' } ]

Solution 4:

You can use for ... in in JavaScript:

for (var key in array) {
    if (/* some condition */) {
        // ...
    }
}

As of JavaScript 1.6, you can use this, too:

for each (var element in array) {
    // ...
}

These are mainly meant to traverse object properties. You should consider to simply use your for-loop.

EDIT: You could use a JavaScript framework like jQuery to eliminate these cross-browser problems. Give it a try. Its $.each()-method does the job.

Solution 5:

You can use Array.prototype.find, wich does exactly what you want, returns the first element fullfilling the condition. Example:

> ([4, {a:7}, 7, {a:5, k:'r'}, 8]).find(o => o.a == 5)

{a:5, k:'r'}