Lookbehind Assertions JavaScript Regular Expressions

Lookbehind allows matching a pattern only if there’re something before.Following is an example −


 Live Demo

<!DOCTYPE html>
<html lang="en">
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
   body {
      font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
   .sample, .result {
      font-size: 20px;
      font-weight: 500;
<h1>Look behind Assertions Regular Expressions</h1>
<div class="sample">The price for 4 tables are $50 , $99 , $121 and $150.</div>
<div style="color: green;" class="result"></div>
<button class="btn">CLICK HERE</button>
Click on the above button to extract the table price using lookbehind
   let sampleEle = document.querySelector(".sample").innerHTML;
   let btnEle = document.querySelector(".btn");
   let resEle = document.querySelector(".result");
   const priceRegex=/(?<=\$)\d+/g;
   btnEle.addEventListener("click", () => {
      resEle.innerHTML = "Table price are = "+sampleEle.match(priceRegex);


The above code will produce the following output −

On clicking the ‘CLICK HERE’ button −

Updated on: 15-Jul-2020


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