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mchelen/index.js

Last active January 31, 2020 20:49
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Javascript ES6 String Prefix Removal 3 Ways
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index.js
/*
How to remove a string prefix based on a delimiter, without knowing the length of the prefix.
#1 substr() + indexOf()
#2 string.split() + array.join()
#3 string.replace() + regex
*/
// example input
const inputString = "search_field:http://www.example.com/welcome:_visitor/index.html"
// const inputString = "search_url:http://www.example.com/welcome:_visitor/index.html"
// const inputString = "homepage:http://www.example.com/welcome:_visitor/index.html"
// #1
let value = inputString
.substr(
inputString.indexOf(':') + 1
);
console.log(value);
// #2
value = inputString
.split(':')
.slice(1)
.join(':');
console.log(value);
// #3
value = inputString
.replace(
/^[^:]+:/,
''
);
console.log(value);
@bengm
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bengm commented Jan 30, 2020

I like #1 since the intent seems clear and straightforward.

#2 is hard to follow, even if effective.

I might like #3 better if I could store the regex in an intuitive/intent-revealing variable name.

@mchelen
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mchelen commented Jan 31, 2020

Yeah, I think I agree for this use case.

#1

  • violates DRY by repeating the variable name
  • when looking at things like inputString.indexOf(':') + 1 it can be hard to tell what that + 1 is doing

#2

  • violates DRY with the delimiter
  • thinking through the split / slice / join steps is more complicated

#3

  • reading regex is usually not intuitive

@bengm
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bengm commented Jan 31, 2020 •
edited

Regarding 3, I'm even thinking something like below could explain the regex via variable name.

everythingBeforeFirstColon = /^[^:]+:/;
value = inputString
  .replace(
    everythingBeforeFirstColon,
    ''
  );
console.log(value);

Adds a line, but could add some clarity vs. mentally parsing what the regex is supposed to do.

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