How do I find an array item with TypeScript? (a modern, easier way)

Question

Is there a canonical way to find an item in an array with TypeScript?

ES6+ allows this simple/clean approach

[{"id":1}, {"id":-2}         


        

Answer 1

Part One - Polyfill

For browsers that haven't implemented it, a polyfill for array.find. Courtesy of MDN.

if (!Array.prototype.find) {
  Array.prototype.find = 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 value;
      }
    }
    return undefined;
  };
}

Part Two - Interface

You need to extend the open Array interface to include the find method.

interface Array {
    find(predicate: (search: T) => boolean) : T;
}

When this arrives in TypeScript, you'll get a warning from the compiler that will remind you to delete this.

Part Three - Use it

The variable x will have the expected type... { id: number }

var x = [{ "id": 1 }, { "id": -2 }, { "id": 3 }].find(myObj => myObj.id < 0);