CODEWITHSUNDEEP
javascript
Kyle Rhodes
Kyle Rhodes

Reputation: 11

begin .map(callback()) from specific index

Is it possible to run a callback function with specific start and stop indexes? I am practicing my JS and am writing a function to convert strings to camel case (from being '-' or '_' seperated) without altering the capitalization of the first word in the string. Basically, after I split the string into an array of words, I want to call .map() and start my callback on the second word in the array. currently I have:

function toCamelCase(str){
  return str.split(/\-|_/).map(word => word.charAt(0).toUpperCase() + word.slice(1)).join('');
}

How can I get .map() to begin at str.split(/\-|_/)[1] ?

Upvotes: 0

Views: 209

Answers (2)

AdityaParab
AdityaParab

Reputation: 7100

In simple words, you can't. .map will iterate over an entire array. You can chain .map to .slice though

function toCamelCase(str, start, stop){
  return str.split(/\-|_/).slice(start, stop).map(word => word.charAt(0).toUpperCase() + word.slice(1)).join('');
}

Upvotes: 2

Ori Drori
Ori Drori

Reputation: 192467

Array.map() always iterates the entire array. You can use the index (2nd param in callback) to return the word without changes if the index is 0:

function toCamelCase(str){
  return str.split(/\-|_/).map((word, i) => i ? word.charAt(0).toUpperCase() + word.slice(1) : word).join('');
}

console.log(toCamelCase('the_camels_toes'));

BTW - you can use a regular expression with String.replace() to to create the camel case:

function toCamelCase(str){
  return str.replace(/_(\w)/g, (_, c) => c.toUpperCase());
}

console.log(toCamelCase('the_camels_toes'));

Upvotes: 0

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