For loops in JavaScript functions

const animals = ["dog", "cat", "tree frog"];

function pluralize(array) {
for (var i = 0; i <= array.length; i++) {
array[i] += "s"
return (array)
}
}
console.log(pluralize(animals));


My goal is to create a function that adds the s to the end of words. However when I ran my code s was only added to the first word in the array. Why was the s not added to the other words in the array?

return

return

i < array.length

array[array.length]

6 Answers
6

var animals = ["dog", "cat", "tree frog"];
function pluralize(array){
for(var i=0;i<=array.length;i++){
array[i] += "s" ;
}
return (array);
}

You are returning in for loop.This is not correct

Use return statement after loop completed.
Also loop shoud iterate from 0 to less than array.length, instead of less than and equal to.

function pluralize(array){
for(var i=0;i<array.length;i++){
array[i] += "s" ;
}
return (array);
}


Please change i<=array.length to i<array.length.

i<=array.length

i<array.length

Otherwise,it will cause infinite loop.

for(var i=0;i<array.length;i++){
array[i] += "s" ;

}
return (array)//take it outside of for loop.
}


const animals = ["dog", "cat", "tree frog"];

function pluralize(array){
for(var i=0;i < array.length;i++){
array[i] += "s"
}
return array;
}

console.log(pluralize(animals));

First of all, your return will be executed on the first loop and exited the loop, which is not what you intended, and hence moving out from loop and place at the end of function.

return

Second, i <= array.length will hit array index outOfBound issues. Reason is array.length == 4 and array[4] += "s" is wrong as you don't have element at array[4].

i <= array.length

array index outOfBound

array.length == 4

array[4] += "s"

array[4]

It's recommended to change the parameter name in your pluralize function from array to something else like arr, purely to improve readability because a very similar word like Array is a keyword/reserve word

pluralize

array

arr

Array

There are multiple problems with your program.

i<=array.length;

for loop

const animals = ["dog", "cat", "tree frog"];
function pluralize(array){
for(var i=0;i<array.length;i++){
array[i] += "s";
}
return (array);
}
console.log(pluralize(animals));

The above program will return appropriate result.

Since you seem to use ES6/20xx, a simple map would do. If you want to mutate the array, use pluralizeMutating.

map

pluralizeMutating

const pluralize = array => array.map(v => `${v}s`);
const pluralizeMutating = array => array.forEach( (v, i) => array[i] += "s" );
let animals = ["dog", "cat", "tree frog"];
console.log(`Pluralized: [${pluralize(animals)}]`);
console.log(`animals Array is not touched: [${animals}]`);
pluralizeMutating(animals);
console.log(`pluralizeMutating ran - animals Array is now: [${animals}]`);

array => array.forEach( ( x, i ) => array[ i ] = pluralize( x ) )

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