const regex = /image(\d\d)$/gm;
// Alternative syntax using RegExp constructor
// const regex = new RegExp('image(\\d\\d)$', 'gm')
const str = `image1
image2
image3
image4
image5
image6
image7
image8
image9
image10
image11
image12
image13
image14
image15
image100
image101
image102
image103
image104
image105`;
const subst = `image0$1`;
// The substituted value will be contained in the result variable
const result = str.replace(regex, subst);
console.log('Substitution result: ', result);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for JavaScript, please visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions