28. JavaScript Fundamentals

Arrow Functions:

function foo() {
  return 10;
}

foo = () => 10;

  obj = {
        id: 42,
        foo: function foo() {
          setTimeout(() => {
              console.log(this.id);
          }, 1000);
        }
  };

  ((foo, p, list1, list2 ) => {
       (foo = (x, y = x * 2) =>
          function bar(z, baz, obj) {
              if (z.length > 3) {
                return z.map( baz = v =>
                  v > 3 ? v + y : baz(v * 4)
                );
              }
              else {
                obj = [];
                setTimeout( () =>
                  obj.length = 1, obj[0] = this.w, 100);
                return obj;
              }
          },
        p = foo(2),
        list1 = [1, 3, 4],
        list2 = list1.concat(6),
        list1 = p.call({ w: 42 }, list1),
        list2 = p(list2),
        setTimeout( () => console.log(list1[0] === list2.reduce((s, v) => s + v, 0)), 200))
})();

Let:

function foo(x, y) {

    try {
      var z = bar(x * 10);
    }
    catch(err) {

    }

      if ( x > y) {
        let tmp = x;
        x = y;
        y = tmp;
      }
      for (let i = 0; i < 10; i++) {
          console.log(i);
      }
      return {'x': x, 'y': y };
}

function bar(a) {
  return a * 100;
}

Const:

    const x = 10;
    const PI = 3.14;
    const y = Object.freeze([0, 1, 2]);

    const x = 2;
const fns = [];

{
      const x = 5;
      for (let i = 0; i < x; i++) {
        fns[i] = (num) => i;
      }

}

console.log( (x * 2) === fns[x*2]());

Default Values:

function foo(x = 42) {
  return x;
}

Lazy Expressions:

function bar() {
  console.log('!!!');
}

function foo(x = bar()) {
}

foo();
foo();
foo();