forEach method in JavaScript + GIVEAWAY

forEach method in JavaScript + GIVEAWAY

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2 min read

The main purpose of forEach method is it executes a provided function once for each array element. In other words, iterates over the array. Often used in functional programming. Always returns undefined.

// SYNTAX: syntax.png

  • arr - The array forEach is iterating on
  • this - A value to use as this when executing callback (optional)
  • callback - A fucntion executed once for each arr element

Argumnet passed to the callback function:

  • currentValue - The current element being processed in the array.
  • index - The index of the current element being processed in the array (optional)
  • arr - The whoole array forEach is iterating on(optional)

Let's do something

let arr = ['a', 'b', 'c', 'd'] 

arr.forEach((el, i, arr) => {
    console.log(el)
}); 

// Logs each string form arr in the console. Let's say we want to log each element in the array until we meet a 'c' character. Then the forEach loop. 

// But actually - there's no way to exit (stop) the while for Each! We can only exit the current iteration. 

// That's when you should go and use a loop. If not, here's a way to do it with forEach:

let meet = true
arr.forEach((el, i, arr) => {
    if (el === 'c') meet = false; 
    if (meet) console.log(el); 
}) // log ['a', 'b']

// now the same thing using a for loop: 
for (let i = 0; i <= arr.length; i++) {
    if (arr[i] === 'c') brake; 
    console.log(arr[i]); 
}

// In this previous situation it was better to just use a loop. Now I will show you a case where it's the opposite. 

let copy = []

// before
for (let i = 0; i < arr.length; i++ ) {
    copy.push(arr[i])
}

// after
arr.forEach( el => copy.push(el))

Facts:-

  • it always returns true
  • expects the callback function to synchronous
  • you can't stop its iteration
  • very powerful when chained with another method
  • support by all modern browsers

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