javascript list find code example

Example 1: js array find

var ages = [3, 10, 18, 20];

function checkAdult(age) {
  return age >= 18;
}
/* find() runs the input function agenst all array components
   till the function returns a value
*/
ages.find(checkAdult);

Example 2: find all of array which satisfy condition javascript

myArray.filter(x => x > 5)

Example 3: javascript array find

// Use array.find() like this:

var myArrayOfAges = [1,4,6,8,9,13,16,21,53,78];

var result = myArrayOfAges.find(age => age >= 12);

console.log(result); // Output: 13

/* ------ Below is a polyfill from Mozilla: ------ */

// https://tc39.github.io/ecma262/#sec-array.prototype.find
if (!Array.prototype.find) {
  Object.defineProperty(Array.prototype, 'find', {
    value: function(predicate) {
      // 1. Let O be ? ToObject(this value).
      if (this == null) {
        throw TypeError('"this" is null or not defined');
      }

      var o = Object(this);

      // 2. Let len be ? ToLength(? Get(O, "length")).
      var len = o.length >>> 0;

      // 3. If IsCallable(predicate) is false, throw a TypeError exception.
      if (typeof predicate !== 'function') {
        throw TypeError('predicate must be a function');
      }

      // 4. If thisArg was supplied, let T be thisArg; else let T be undefined.
      var thisArg = arguments[1];

      // 5. Let k be 0.
      var k = 0;

      // 6. Repeat, while k < len
      while (k < len) {
        // a. Let Pk be ! ToString(k).
        // b. Let kValue be ? Get(O, Pk).
        // c. Let testResult be ToBoolean(? Call(predicate, T, « kValue, k, O »)).
        // d. If testResult is true, return kValue.
        var kValue = o[k];
        if (predicate.call(thisArg, kValue, k, o)) {
          return kValue;
        }
        // e. Increase k by 1.
        k++;
      }

      // 7. Return undefined.
      return undefined;
    },
    configurable: true,
    writable: true
  });
}

Example 4: find a single element in array of objects javascript

myArray.find(x => x.id === '45').foo;