Loop : for in & for of

for ...in loop

• Can only access 'key' of an object

• Repeat all iterable properties of an object

    var obj = {
        "a": 1,
        "b": 2,
        "c": 3
    }
  
    for (var prop in obj) {
        console.log(`${prop}: ${obj[prop]}`)
        // a: 1
        // b: 2
        // c: 3
    }
  

for ...of loop

• ES6

• Whole collection needs [Symbol.iterator] property

    // example 1
    var obj = {
        "a": 1,
        "b": 2,
        "c": 3
    }
  
    for (var key of Object.keys(obj) {
        console.log(`${key}: ${obj[key]}`)
        // a: 1
        // b: 2
        // c: 3
    }
  
    // exampe 2
    var iterable = [10, 20, 30];
  
    for (var value of iterable) {
        console.log(value);
        // 10
        // 20
        // 30
    }