Tips for locating the index of a substring within a string with varying line endings using Typescript

Question

Tips for locating the index of a substring within a string with varying line endings using Typescript

I am faced with the task of comparing two strings together.

abc\r\ndef

c\nde

My goal is to determine the index of string 2 within string 1.

Using the indexOf() method is not an option due to different line endings, so I require an alternative solution that takes this into account.

It's important that I do not alter the original string as I need the substring index in reference to the original. Simply replacing all instances of \r\n with \n would disrupt the original indexes, necessitating a restoration process.

javascript typescript string substring line-endings

Answer 1

Answer №1

(For what it's worth, there's no need for TypeScript in this question. It's all about JavaScript.)

To achieve this, you can convert the target string into a regular expression by using the alternation \r\n|\r|\n wherever these sequences appear. Make sure to escape the parts in-between (refer to this question's answers for assistance). When you use the `exec` method of the resulting regex on the initial string, if it finds a match, the result (referred to as `match`) will contain the index at `match.index` and the matched text at `match[0]`.

Here is an example with TypeScript type annotations commented out:

// Adapted from https://stackoverflow.com/a/3561711/157247
function escapeRegex(string) {
    return string.replace(/[/\-\\^$*+?.()|[\]{}]/g, '\\$&');
}

function test(str/*: string */, substr/*: string*/) {
    // Break down the text based on newline sequences,
    // escape the parts in-between,
    // then combine them with an alternation
    const rexText = substr
        .split(/\r\n|\n|\r/)
        .map((part) => escapeRegex(part))
        .join("\\r\\n|\\n|\\r");
    // Create the regex
    const re = new RegExp(rexText);
    // Execute it
    const match = re.exec(str);
    if (match) {
        console.log(`Found ${JSON.stringify(match[0])} at index ${match.index} in ${JSON.stringify(str)}`);
    } else {
        console.log(`Not found`);
    }
}


test("abc\r\ndef", "c\nde");

Answer 2

(For what it's worth, there's no need for TypeScript in this question. It's all about JavaScript.)

To achieve this, you can convert the target string into a regular expression by using the alternation \r\n|\r|\n wherever these sequences appear. Make sure to escape the parts in-between (refer to this question's answers for assistance). When you use the `exec` method of the resulting regex on the initial string, if it finds a match, the result (referred to as `match`) will contain the index at `match.index` and the matched text at `match[0]`.

Here is an example with TypeScript type annotations commented out:

// Adapted from https://stackoverflow.com/a/3561711/157247
function escapeRegex(string) {
    return string.replace(/[/\-\\^$*+?.()|[\]{}]/g, '\\$&');
}

function test(str/*: string */, substr/*: string*/) {
    // Break down the text based on newline sequences,
    // escape the parts in-between,
    // then combine them with an alternation
    const rexText = substr
        .split(/\r\n|\n|\r/)
        .map((part) => escapeRegex(part))
        .join("\\r\\n|\\n|\\r");
    // Create the regex
    const re = new RegExp(rexText);
    // Execute it
    const match = re.exec(str);
    if (match) {
        console.log(`Found ${JSON.stringify(match[0])} at index ${match.index} in ${JSON.stringify(str)}`);
    } else {
        console.log(`Not found`);
    }
}


test("abc\r\ndef", "c\nde");

Tips for locating the index of a substring within a string with varying line endings using Typescript

Answer №1

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