Node.js by Example: For

for loops exist in JavaScript to help iterator over items.

The most basic type, with three expressions.

 
for (let i = 1; i <= 3; i++) {
    console.log(i);
}

All three expressions in the head of the for loop are optional. For example, it is not required to use the initialization block to initialize variables:

 
let i = 1;
for (; i < 3; i++) {
  console.log(i);
}

A while loop will iterate until the given expression is false.

 
let a = 0;
while (a <= 3) {
  console.log('while', a);
  a++;
}

A do...while will perform one iteration then continue looping while the expression is true.

 
let b = 0;
do {
    console.log('do-while', b);
    b++;
} while (b % 2 !== 0);

The for...in statement iterates over all enumerable string properties of an object (ignoring properties keyed by symbols), including inherited enumerable properties.

 
let object = { a: 1, b: 2, c: 3 };
for (let property in object) {
  console.log(`${property}: ${object[property]}`);
}

The for...of statement executes a loop that operates on a sequence of values sourced from an iterable object.

 
let array = ["a", "b", "c"];
for (let element of array) {
  console.log(element);
}
 
$ node for.js
1
2
3
1
2
while 0
while 1
while 2
while 3
do-while 0
do-while 1
a: 1
b: 2
c: 3
a
b
c

Next example: .

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