javascript - remove array element on condition

I was wondering how I'd go about implementing a method in javascript that removes all elements of an array that clear a certain condition. (Preferably without using jQuery)

Ex.

ar = [ 1, 2, 3, 4 ];
ar.removeIf( function(item, idx) {
    return item > 3;
});

The above would go through each item in the array and remove all those that return true for the condition (in the example, item > 3).

I'm just starting out in javascript and was wondering if anyone knew of a short efficient way to get this done.

--update--

It would also be great if the condition could work on object properties as well.

Ex.

ar = [ {num:1, str:"a"}, {num:2, str:"b"}, {num:3, str:"c"} ];
ar.removeIf( function(item, idx) {
    return item.str == "c";
});

Where the item would be removed if item.str == "c"

--update2--

It would be nice if index conditions could work as well.

Ex.

ar = [ {num:1, str:"a"}, {num:2, str:"b"}, {num:3, str:"c"} ];
ar.removeIf( function(item, idx) {
    return idx == 2;
});

You can use Array filter method.

The code would look like this:

ar = [1, 2, 3, 4];
ar = ar.filter(item => !(item > 3));
console.log(ar) // [1, 2, 3]

You could add your own method to Array that does something similar, if filter does not work for you.

Array.prototype.removeIf = function(callback) {
    var i = 0;
    while (i < this.length) {
        if (callback(this[i], i)) {
            this.splice(i, 1);
        }
        else {
            ++i;
        }
    }
};

To me, that's one of the coolest features of JavaScript. Ian pointed out a more efficient way to do the same thing. Considering that it's JavaScript, every bit helps:

Array.prototype.removeIf = function(callback) {
    var i = this.length;
    while (i--) {
        if (callback(this[i], i)) {
            this.splice(i, 1);
        }
    }
};

This avoids the need to even worry about the updating length or catching the next item, as you work your way left rather than right.

You can use Array.filter(), which does the opposite:

ar.filter(function(item, idx) {
    return item <= 3;
});

You can use lodash.remove

var array = [1, 2, 3, 4];
var evens = _.remove(array, function(n) {
  return n % 2 == 0;
});
 
console.log(array);
// => [1, 3]
 
console.log(evens);
// => [2, 4]

Make it a one-liner with arrow function:

ar = ar.filter(i => i > 3);

I love these kinds of questions and just a different version from me too... :)

Array.prototype.removeIf = function(expression) {
   var res = [];
    for(var idx=0; idx<this.length; idx++)
    {
      var currentItem = this[idx];
        if(!expression(currentItem))
        {
            res.push(currentItem);
        }
    }
    return res;
}

ar = [ 1, 2, 3, 4 ];
var result = ar.removeIf(expCallBack);


console.log(result);
function expCallBack(item)
{
    return item > 3;
}

simply write the following example if condition could work on object properties as well

var ar = [ {num:1, str:"a"}, {num:2, str:"b"}, {num:3, str:"c"} ];
var newArray = [];
for (var i = 0, len = ar.length; i<len; i++) {
        if (ar[i].str == "b") 
        {newArray.push(ar[i]);};
 };
console.log(newArray);

See the example Live Example

if you need to remove exactly one item, and you know for sure that the item exists, you can use this one-liner:

ar.splice(ar.findIndex(el => el.id === ID_TO_REMOVE), 1);

// or with custom method:
let ar = [ {id:1, str:"a"}, {id:2, str:"b"}, {id:3, str:"c"}, {id:4,str:"d"} ];
ar.removeById = id => ar.splice(ar.findIndex(el => el.id === id), 1);
ar.removeById(ID_TO_REMOVE);

http://jsfiddle.net/oriadam/72kgprw5/

ES6 only

My solution for an array of numbers would be:

ar.filter(item => item < 4);

For the in-place remove, my solution is

ar.filter(item => !(item > 3))
  .forEach(obsoleteItem => ar.splice(ar.indexOf(obsoleteItem), 1));