Get and replace the last number on a string with JavaScript or jQuery

Question

If I have the string:

var myStr = \"foo_0_bar_0\";

and I guess we should have a function called getAndIncrementLastNumber(str)

Answer 1

@Brilliant is right, +1, I just wanted to provide a version of his answer with 2 modifications:

• Remove the unnecessary negative look-ahead operator.
• Add the ability to add a number in the end, in case it doesn't exist.

```

/**
 * Increments the last integer number in the string. Optionally adds a number to it
 * @param {string} str The string
 * @param {boolean} addIfNoNumber Whether or not it should add a number in case the provided string has no number at the end
 */
function incrementLast(str, addIfNoNumber) {
    if (str === null || str === undefined) throw Error('Argument \'str\' should be null or undefined');
    const regex = /[0-9]+$/;
    if (str.match(regex)) {
        return str.replace(regex, (match) => {
            return parseInt(match, 10) + 1;
        });
    }
    return addIfNoNumber ? str + 1 : str;
}

Tests:

describe('incrementLast', () => {
        it('When 0', () => {
            assert.equal(incrementLast('something0'), 'something1');
        });
        it('When number with one digit', () => {
            assert.equal(incrementLast('something9'), 'something10');
        });
        it('When big number', () => {
            assert.equal(incrementLast('something9999'), 'something10000');
        });
        it('When number in the number', () => {
            assert.equal(incrementLast('1some2thing9999'), '1some2thing10000');
        });
        it('When no number', () => {
            assert.equal(incrementLast('1some2thing'), '1some2thing');
        });
        it('When no number padding addIfNoNumber', () => {
            assert.equal(incrementLast('1some2thing', true), '1some2thing1');
        });
    });