How many loop methods are there in js? Introduction to seven loop methods in js (with code)

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JavaScript provides many methods for iterating through LOOPS. This tutorial explains the wide variety of looping possibilities in modern JAVASCRIPT

Introduction

JavaScript provides many ways to iterate over loops. This tutorial explains each one through a small example and main properties.

for

const list = ['a', 'b', 'c']
for (let i = 0; i < list.length; i++) {
  console.log(list[i]) //value
  console.log(i) //index
}

• You can use break to interrupt the for loop

• You can use continue to continue the next iteration of the for loop

forEach

Introduced in ES5. Given an array, you can iterate over its properties using list.forEach():

const list = ['a', 'b', 'c']
list.forEach((item, index) => {
  console.log(item) //value
  console.log(index) //index
})

//index is optional
list.forEach(item => console.log(item))

Note though that you can't get out of this loop.

do...while

const list = ['a', 'b', 'c']
let i = 0
do {
  console.log(list[i]) //value
  console.log(i) //index
  i = i + 1
} while (i < list.length)

You can use break to interrupt the while loop:

do {
  if (something) break
} while (true)

You can use continue to jump to the next iteration:

do {
  if (something) continue

  //do something else
} while (true)

while

const list = ['a', 'b', 'c']
let i = 0
while (i < list.length) {
  console.log(list[i]) //value
  console.log(i) //index
  i = i + 1
}

You can use break to interrupt the while loop:

while (true) {
  if (something) break
}

You can use continue to jump to the next iteration:

while (true) {
  if (something) continue

  //do something else
}

The difference with do...while The point is that do...while always executes the loop at least once.

for...in

Iterate over all enumerable properties of the object, giving the property name.

for (let property in object) {
  console.log(property) //property name
  console.log(object[property]) //property value
}

for...of

ES2015 introduces the for loop, which combines the simplicity and cracking capabilities of forEach:

//iterate over the value
for (const value of ['a', 'b', 'c']) {
  console.log(value) //value
}

//get the index as well, using `entries()`
for (const [index, value] of ['a', 'b', 'c'].entries()) {
  console.log(index) //index
  console.log(value) //value
}

Be careful to use const. This loop creates a new range on each iteration, so we can safely use it instead of let.

for...in VS FOR...OF The difference between

and for...in is:

• for...of Iteration attribute value

• for...in Iteration attribute name

Related recommendations:

for of js Analysis of the difference between in loop and foreach loop in java

Understanding JS event loop_javascript skills

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