Regex match from array of strings in JavaScript

Question

I am facing a bit problem in Regex. I want to find the start and end index of the complete matched string in the input string.

e.g. I have an array of strings like

["a", "aa"]

and I have a text like I like a problem aa

I am doing with iteration of array strings.

let arr = ["a", "aa"];
let str = "I like a problem aa";
let indicesArr = [];
arr.forEach(a=>{
 const regexObj = new RegExp(a, "gi");
 let match;
 while ((match = regexObj.exec(str))) {
 let obj = { start: match.index, end: regexObj.lastIndex }
 indicesArr.push(obj);
 if(!match.index || !regexObj.lastIndex) break;
 }
});

above code gives me the result

[
 {start: 7, end: 8},
 {start: 17, end: 18},
 {start: 18, end: 19},
 {start: 17, end: 19}
]

I want the result should be

[
 {start: 7, end: 8},
 {start: 17, end: 19}
]

Any suggestion would be very helpful, thanks:)

• Wiktor Stribiżew: Use word boundaries to match a whole word, not a partial match.
• abinas patra: Hey, thank you so much for the suggestion,but if my string is I like a problem aa and aaaa, actually it's not matching the last aaaa part.
• Wiktor Stribiżew: Then you need to use a aa|a regex.
• abinas patra: I am not getting, can you please write a small example, it would be helpful thanks:)
• Wiktor Stribiżew: See jsfiddle.net/wiktor_stribizew/jomL13rq

Answer 1

The problem here is that a finds two matches in aa. You need to make sure you match all occurrences of a regex that finds either aa or a in this order. It means, the regex must be /aa|a/g and not /a|aa/g as the order of alternation matters in regex.

Here, you can use

let arr = ["a", "aa"];
let str = "I like a problem aa";
let indicesArr = [];
arr.sort((a, b) => b.length - a.length);
const regexObj = new RegExp(arr.map(x=> x.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&')).join('|'), "gi");
let match;
while (match = regexObj.exec(str)) {
 let obj = { start: match.index, end: regexObj.lastIndex }
 indicesArr.push(obj);
}
console.log(indicesArr);

Note these two lines:

• arr.sort((a, b) => b.length - a.length); - sorts the arr items by length in the descending order (to put aa before a)
• const regexObj = new RegExp(arr.map(x=> x.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&')).join('|'), "gi"); - escapes all items in the arr array for use inside a regex, and joins the items with | alternation operator into a single string regex pattern.