indexOf() when array-elements are objects (javascript)

Question

For instance, a variable named arrayElements of type array contains:
[{id:1, value:5},{id:2, value:6},{id:3, value:7},{id:4, value:8}].

How do I get the position of the array element with id === 3(3rd element) in the arrayElements variable besides using loop?

thanks.

Answer 1

You have to loop at one point. But you can abstract it to look like you're not looping

function indexOfCallback(arr, callback, startIndex) {
    if (typeof startIndex == 'undefined') {
        startIndex = 0;
    }
    for(var i=startIndex; i < arr.length; i ++) {
        if (callback(arr[i])) {
            return i;
        }
    }
    return -1;
}

var array = [{id:1, value:5},{id:2, value:6},{id:3, value:7},{id:4, value:8}];
// Search on id === 3
console.log(indexOfCallback(array, function(obj){
    return obj.id === 3;
}));
// Search on value === 6
console.log(indexOfCallback(array, function(obj){
    return obj.value === 6;
}));

As mentioned by Anthony, this is proposed for ECMAScript 6. Here's the more complete polyfill https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/findIndex

if (!Array.prototype.findIndex) {
  Array.prototype.findIndex = function(predicate) {
    if (this == null) {
      throw new TypeError('Array.prototype.find called on null or undefined');
    }
    if (typeof predicate !== 'function') {
      throw new TypeError('predicate must be a function');
    }
    var list = Object(this);
    var length = list.length >>> 0;
    var thisArg = arguments[1];
    var value;

    for (var i = 0; i < length; i++) {
      value = list[i];
      if (predicate.call(thisArg, value, i, list)) {
        return i;
      }
    }
    return -1;
  };
}
console.log(array.findIndex(function(obj){
    return obj.id === 3;
}));