Extract substring from between two words

Question

I'm trying to find a clean way to extract a substring from between two other substrings.So far I can do it based on targeting a specific character, but not a string. E.g (this doesn't work)

 var element = "Firstconstantmystring_lastconstant";
 var mySubString = element.substring(
                            element.lastIndexOf("Firstconstant") + 1,
                            element.lastIndexOf("_lastconstant")
                        );

I'm trying to extract "mystring" from the full string. I know that "Firstconstant" and "_lastconstant" will always be the same. Grateful for any help.

shreyasm-dev · Accepted Answer · 2020-10-10 16:51:09Z

3

You can use a regular expression.

var string = 'Firstconstantmystring_lastconstant'
console.log(string.match(/(?<=Firstconstant)[\s\S]*(?=_lastconstant)/))

This will return an array with the first element being the result you want if there is a match, or null if there is no match.

Resources:

MDN Reference for String.prototype.match: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/match
MDN regex cheatsheet: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions/Cheatsheet

answered Oct 10, 2020 at 16:51

shreyasm-dev

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1 Comment

Mamun Over a year ago

You should also mention about the performance between substring and regex!!!

Mamun · Accepted Answer · 2020-10-10 16:51:19Z

1

You should take the length from the first:

var element = "Firstconstantmystring_lastconstant";
var mySubString = element.substring(
                            "Firstconstant".length,
                            element.lastIndexOf("_lastconstant")
                        );
console.log(mySubString);

answered Oct 10, 2020 at 16:51

Mamun

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Comments

Shohanur · Accepted Answer · 2020-10-10 17:09:50Z

1

function substringBetween(s, a, b) {
var p = s.indexOf(a) + a.length;
return s.substring(p, s.indexOf(b, p));
}

var element = "Firstconstantmystring_lastconstant;";
var mySubString = substringBetween(element,'Firstconstant','_lastconstant')

console.log({mySubString })

answered Oct 10, 2020 at 17:09

Shohanur

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