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

by

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<T> {
    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);

More Related Contents:

  1. How do I dynamically assign properties to an object in TypeScript?
  2. What is “not assignable to parameter of type never” error in TypeScript?
  3. Is it possible to restrict TypeScript object to contain only properties defined by its class?
  4. Expected 3 type arguments but got 1 but it should infer 2 types
  5. Import class in definition file (*d.ts)
  6. TypeScript union of string and string literals
  7. Are strongly-typed functions as parameters possible in TypeScript?
  8. What does the `is` keyword do in typescript?
  9. Why can I avoid excess property check in typescript just by passing a reference to an object to a function rather than the object in its literal form?
  10. TypeScript: Accept all Object keys that map to a specific type
  11. Typescript interface default values
  12. How to configure custom global interfaces (.d.ts files) for TypeScript?
  13. TypeScript – use correct version of setTimeout (node vs window)
  14. Is there a way to “extract” the type of TypeScript interface property?
  15. TypeScript error TS1005: ‘;’ expected (II)
  16. Is there an option to make spreading an object strict?
  17. Circular Type References in TypeScript
  18. ‘compile-time’ way to get all property names defined interface
  19. Make overProp function interface with one param
  20. TypeScript: Why can’t I assign a valid field of an object with type { a: “a”, b: “b” }
  21. Absolute paths (baseUrl) gives error: Cannot find module
  22. typescript restrict count of object’s properties
  23. TypeScript keyof returning specific type
  24. Why is never assignable to every type?
  25. Is there an alternative to Partial to accept only fields from another type and nothing else?
  26. Setting up tsconfig with spec/test folder
  27. Does TypeScript allow type aliases?
  28. How to pass an instance variable into typescript decorator arguments?
  29. Can I force the TypeScript compiler to use nominal typing?
  30. Optional class members in Typescript

Leave a Comment