JavaScript Array

forEach

The forEach() method executes a provided function once for each array element.

usage:

forEach(() => {...})
forEach((value) => {...})
forEach((value,key) => {...})
forEach((value,key,array) => {...})

example:

const arrayExample = ['a','b','c','d']

//forEach((value) => {...})
arrayExample.forEach((e)=>{
    console.log(e);
})
//output: 'a'
//output: 'b'
//output: 'c'
//output: 'd'

//forEach((value,key) => {...})
arrayExample.forEach((e,i)=>{
    console.log(e,i);
})
//output: 'a' 0
//output: 'b' 1
//output: 'c' 2
//output: 'd' 3

//forEach((value,key,array) => {...})
arrayExample.forEach((e,i,arr)=>{
    console.log(e,i,arr);
})
//output: 'a' 0 ['a','b','c','d']
//output: 'b' 1 ['a','b','c','d']
//output: 'c' 2 ['a','b','c','d']
//output: 'd' 3 ['a','b','c','d']

map

The map() method creates a new array populated with the results of calling a provided function on every element in the calling array.

usage:

map(() => {...})
map((element) => {...})
map((element,key) => {...})
map((element,key,array) => {...})

example:

const arrayExample = ['a','b','c','d']

//map((value) => {...})
const arrayMap = arrayExample.map((x)=>(`Get: ${x}`));
console.log(arrayMap)
//output: [ 'Get: a', 'Get: b', 'Get: c', 'Get: d' ]

//const arrayMap = map((value,key) => {...})
const arrayMap = arrayExample.map((x,i)=>(`Index ${i}: ${x}`));
console.log(arrayMap)
//output: [ 'Index 0: a', 'Index 1: b', 'Index 2: c', 'Index 3: d' ]

//const arrayMap = map((value,key,array) => {...})
const arrayMap = arrayExample.map((x,i,arr)=>(`Index ${i}: ${x} by ${arr}`));
console.log(arrayMap)
/*output: [
  'Index 0: a by a,b,c,d',
  'Index 1: b by a,b,c,d',
  'Index 2: c by a,b,c,d',
  'Index 3: d by a,b,c,d'
]*/

filter

The filter() method creates a new array with all elements that pass the test implemented by the provided function.

usage:

filter((element) => {...})
filter((element,key) => {...})
filter((element,key,array) => {...})

example:

const arrayExample = ['apple','banana','coconut','grape','grapefruit']

//filter((element) => {...})
const arrayFilter = arrayExample.filter((x)=>(x.length > 5));
console.log(arrayFilter)
//output: [ 'banana', 'coconut', 'grapefruit' ]

//filter((element,key) => {...})
const arrayFilter = arrayExample.filter((x,i)=>(i%2==0));
console.log(arrayFilter)
//output: [ 'apple', 'coconut', 'grapefruit' ]

Reference:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array

tags: javascript