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Javascript – Match values in-between braces

I have a string like this: "hello %{name} good %{middle} bye".

I’m trying to find an effective way to extract out the values in-between the braces, so ideally I would end up with an array of ["name", "middle"].

Using match I can almost get there. The following returns: ['%{name}', '%{middle}']:

"hello %{name} good %{middle} bye".match(/%{([w]+)}/g)

I’m not sure why it’s including the %, {, and } characters in the return though.

How can I adjust my regular expression to only match name and middle?

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3

Answers


  1. 0

    You can use a named capturing group. In the example below, we name it value, and then extract those values during iteration of the regex matches:

    let s = "hello %{name} good %{middle} bye"

let r = [...s.matchAll(/%{(?<value>[w]+)}/g)].map(i => i.groups.value)

console.log(r)
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  2. 0

    Try

    const str = "hello %{name} good %{middle} bye";
const regex = /%{([w]+)}/g;
let matches;
const result = [];

while ((matches = regex.exec(str)) !== null) {
  result.push(matches[1]);
}

console.log(result) // [ 'name', 'middle', 'another', 'example' ]

    Regards your question why is it including the %, {, and } characters in the return

    because the match() function in JavaScript returns the entire matched substring, including the %{ and }.

    A solution to this would be to use match[1] (or equivalent in a loop with exec()) allows you to access only the content captured within the parentheses ( ) in your regex pattern.

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  3. 0

    You need to change your regex expression to capture the values inside the braces without the %, {, and } characters, you can modify it slightly.

    Existing: /%{([w]+)}/g => /%{(w+)}/g

    Refer the below examples:

    const str = "hello %{name} good %{middle} bye";
const str1 = "hello %{aaa} good %{bbbb} bye";
const str2 = "hello %{xyz} %{gtr} %{pqr} bye";

const matches = str.match(/%{(w+)}/g);
const matches1 = str1.match(/%{(w+)}/g);
const matches2 = str2.match(/%{(w+)}/g);

const values = matches.map(match => match.slice(2, -1));
const values1 = matches1.map(match => match.slice(2, -1));
const values2 = matches2.map(match => match.slice(2, -1));

console.log(JSON.stringify(values));
console.log(JSON.stringify(values1));
console.log(JSON.stringify(values2));

    Also, this can be achieved via non regex-based approach as well:

    const str = "hello %{name} %{world} %{middle} bye";
const str1 = "hello %{aaa} %{bye} %{bbbb} bye";
const str2 = "hello %{xyz} %{gtr} %{pqr} bye";
const startDelimiter = "%{";
const endDelimiter = "}";

function extractValues(input, startDelimiter, endDelimiter) {
    const values = [];
    let startIndex = 0;

    while ((startIndex = input.indexOf(startDelimiter, startIndex)) !== -1) {
        startIndex += startDelimiter.length;
        const endIndex = input.indexOf(endDelimiter, startIndex);
        if (endIndex === -1) {
            break; 
        }
        const value = input.substring(startIndex, endIndex);
        values.push(value);
        startIndex = endIndex + endDelimiter.length;
    }

    return values;
}

const result = extractValues(str, startDelimiter, endDelimiter);
const result1 = extractValues(str1, startDelimiter, endDelimiter);
const result2 = extractValues(str2, startDelimiter, endDelimiter);


console.log(JSON.stringify(result));
console.log(JSON.stringify(result1)); 
console.log(JSON.stringify(result2));
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