You Don’t Need Loops in JavaScript

Learn how to remove loops and use higher-order functions like map, reduce, and filter

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Why Are We Replacing Loops?

Using higher-order functions will make your code :

• More readable.
• Easy to understand.
• Easy to debug.

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1. To Loop Through All Elements and Get an new modified array

Using loop:

var names = ["Jack", "Jecci", "Ram", "Tom"];

var upperCaseNames = [];

for(let i=0, totalNames = names.length; i< totalNames ; i= i +1) {
    upperCaseNames = names[i].toUpperCase();
}

Without loop:

var names = ["Jack", "Jecci", "Ram", "Tom"];

var upperCaseNames = names.map(name => name.toUpperCase());

Note: If you’re using map, you cannot break or continue or return while looping. For this case, you should use every or some. Read about every and some in this article.

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2. Loop through all elements and perform an action

Using loops

function print(name) {
   console.log(name);
}

var names = ["Jack", "Jecci", "Ram", "Tom"];

for(let i=0, totalNames = names.length; i< totalNames ; i= i +1) {
    print(names[i])
}

without loop

var names = ["Jack", "Jecci", "Ram", "Tom"];

names.forEach(name=> print(name));

3. Filtering Array

Using normal for loop:

function isOdd(n) {
   return n %2;
}

var numbers = [1,2,3,4,5];

var odd = [];

for(let i=0, total = numbers.length; i< total ; i= i +1) {

   let number = numbers[i];
   if( isOdd(number) ) {
      odd.push(number);
   }

}

Using filter:

var numbers = [1,2,3,4,5, 6, 7]

var odd = numbers.filter(n => n%2); // single line

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4. Creating an Output With Array Elements

Sum of numbers:

var numbers = [1,2,3,4,5]

var result = 0;

for(let i=0, total = numbers.length; i< total ; i= i +1) {

   result = result + numbers[i];

}

Using reduce:

var numbers = [1,2,3,4,5,6,7];

function sum(accumulator, currentValue){
   return accumulator + currentValue;
}

var initialVal = 0;
var result = numbers.reduce(sum, initialVal);

The above code can be even more simplified:

var numbers = [1,2,3,4,5,6,7, 10];

var result = numbers.reduce((acc, val)=> acc+val, 0);

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5. Checking if an Array Contains a Value

var names = ["ram", "raj", "rahul"];

for(let i=0, totalNames = names.length; i< totalNames ; i= i +1) {
   if(names[i] === "rahul") {
     console.log("%c found rahul", "color:red");
     return; 
   }
}

Using some:

var names = ["ram", "raj", "rahul"];

let isRahulPresent = names.some(name => name==="rahul");

if(isRahulPresent) {
  console.log("%c found rahul", "color:red"); 
}

%c in the console statement will apply style to the console text. You can learn more about that in this article.

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5. To Check Whether Every Element in an Array Meets a Condition

Using for loop:

var num = [1,2,3,4,5, 0];

for(let i=0, total = numbers.length; i< total ; i= i +1) {

    if(num <= 0) {

      break;
      console.log("0 present in array");
    }
}

Using every:

var num = [1,2,3,4,5, 0];

var isZeroFree = num.every(e => e > 0);

if(!isZeroFree) {
    console.log("0 present in array");
}

Thanks for reading. I hope you like this.