For Loop
You should use for loop, when You know, how many times is gonna run. How many iteration’s gonna have. Use a while loop, when you don’t.
for(let i = 0; i <= 10; i++){ console.log('Number ' + i); }
Continue statement
for(let i = 1; i <= 5; i++){ if(i === 3){ console.log('3 is my favorite number'); continue; } console.log('Number ' + i); }
Number 1 Number 2 3 is my favorite number Number 4 Number 5
Break statement
for(let i = 1; i <= 5; i++){ if(i === 3){ console.log('3 is my favorite number'); continue; } if(i === 4){ console.log('Stop the loop'); break; } console.log('Number ' + i); }
Number 1 Number 2 3 is my favorite number Stop the loop
While Loop
let i = 0; while(i <= 10){ console.log('Number ' + i); i++; }
Do While Loop
It’s always gonna run at least once, no matter what.
let i = 0; do{ console.log('Number ' + i); i++; } while(i < 100);
Loop through array
For Loop
const cars = ['Ford', 'KIA', 'Toyota', 'Honda']; for(let i = 0; i < cars.length; i++){ console.log(cars[i]); }
Ford KIA Toyota Honda
Foreach Array Loop
cars.forEach(function(car){ console.log(car); });
Ford KIA Toyota Honda
Access to key value pairs
cars.forEach(function(car, index){ console.log(`${index} : ${car}`); });
0 : Ford 1 : KIA 2 : Toyota 3 : Honda
Map
We also have a method called map. It’s basically used to return different array.
const users = [ {id:1, name: 'John'}, {id:2, name: 'Jack'}, {id:3, name: 'James'} ]; const ids = users.map(function(user){ return user.id; }); console.log(ids)
const names = users.map(function(user){ return user.name; }); console.log(names);
For in loop – Which is often used for objects
Let’s create a single object called user
const user = { firstName: 'John', lastName: 'Jack', age: 36 }
Access to key
for(let x in user){ console.log(x); }
firstName lastName age
Access to the object with key value paris
for(let x in user){ console.log(`${x} : ${user[x]}`); }
firstName : John lastName : Jack age : 36
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