JavaScript | Throttling

Last Updated : 08 Jun, 2020

Throttling or sometimes is also called throttle function is a practice used in websites. Throttling is used to call a function after every millisecond or a particular interval of time only the first click is executed immediately.

Let’s see, what will happen if throttle function is not Present in the web page. Then the number of times a button is clicked the function will be called the same number of times. Consider the example.

Without throttling Function: In this code suppose if the button is clicked 500 times then the function will be clicked 500 times this is controlled by a throttling function.

Program:

HTML

<!DOCTYPE html> 
<html lang="en"> 
    <head> 
        <meta charset="UTF-8" /> 
        <meta name="viewport" 
              content="width=device-width,  
                       initial-scale=1.0" /> 
        <title> 
          JavaScript | Without Throttling 
        </title> 
    </head> 
    <body> 
        <button id="nothrottle">Click Me</button> 
        <script> 
            
            // Selected button with th egiven id 
            const btn = document.querySelector("#nothrottle"); 
            
            // Add event listener to the button  
            // to listen the click event 
            btn.addEventListener("click", () => { 
                console.log("button is clicked"); 
            }); 
        </script> 
    </body> 
</html> 

Outout:

With Throttling function: In this code if a user continues to click the button every click is executed after 1500ms except the first one which is executed as soon as the user clicks on the button.

Program:

HTML

<!DOCTYPE html> 
<html lang="en"> 
<head> 
  <meta charset="UTF-8"> 
  <meta name="viewport" 
        content="width=device-width, initial-scale=1.0"> 
  <title> 
    JavaScript | With Throttling 
  </title> 
</head> 
<body> 
  <button id="throttle">Click Me</button> 
  <script> 
    const btn=document.querySelector("#throttle"); 
      
    // Throttling Function 
    const throttleFunction=(func, delay)=>{ 
  
      // Previously called time of the function 
      let prev = 0;  
      return (...args) => { 
        // Current called time of the function 
        let now = new Date().getTime();  
  
        // Logging the difference between previously  
        // called and current called timings 
        console.log(now-prev, delay);  
          
        // If difference is greater than delay call 
        // the function again. 
        if(now - prev> delay){  
          prev = now; 
  
          // "..." is the spread operator here  
          // returning the function with the  
          // array of arguments 
          return func(...args);   
        } 
      } 
    } 
    btn.addEventListener("click", throttleFunction(()=>{ 
      console.log("button is clicked") 
    }, 1500)); 
  </script> 
</body> 
</html> 