call function on change of value inside <p> tag

Question

Is there any way in JavaScript by which I can call a function when the value of a paragraph tag is changed.

Overview:

HTML:

<p id="timer">00:00</p>
<button onclick="change()">My Button</button>

JS:

function change() {
  document.getElementById("timer").innerHTML = "00:01";
}

function hello() {
  alert("Hello");
}

I want to alert("Hello") when the value of paragraph is changed. Something like a continuous function checking for a change in the value of paragraph.

Answer 1

You can use MutationObserver with characterData option set to true

 <script> function change() { document.getElementById("timer").innerHTML = "00:01"; } function hello() { alert("Hello"); } window.onload = function() { var target = document.querySelector("p"); var observer = new MutationObserver(function(mutations) { mutations.forEach(function(mutation) { hello() }); }); var config = { childList: true, subtree: true, characterData: true }; observer.observe(target, config); } </script> <p id="timer">00:00</p> <button onclick="change()">My Button</button> 

Answer 2

Try this MutationObserver API, (Check this simple example as well)

var observer = new MutationObserver(function(mutations) {
    mutations.forEach(function(mutation) {
        //value changed, call the other API
        hello();
    });    
});
var observerConfig = {
    characterData: true //since only the node-value needs to be checked in your case
}; 
var targetNode = document.getElementById("timer");
observer.observe(targetNode, observerConfig);

DEMO

 var MutationObserver = window.MutationObserver || window.WebKitMutationObserver || window.MozMutationObserver; var observer = new MutationObserver(function(mutations) { mutations.forEach(function(mutation) { //value changed, call the other API if ( mutation.type="childList" ) { hello(); //observer.disconnect(); } }); }); var observerConfig = { childList: true }; var targetNode = document.body; observer.observe(targetNode, observerConfig); document.getElementById("timer").innerHTML = "0.2"; window.hello = function (){ alert(1); } 

 <p id="timer">0.0</p> 

Answer 3

One more option to do this

 function change() { document.getElementById("timer").innerHTML = new Date().getTime(); } var prevValue = document.getElementById("timer").innerHTML; setInterval(function() { currValue = document.getElementById("timer").innerHTML; if (prevValue != currValue) { prevValue = currValue; hello(); } }, 1); function hello() { alert("Hello"); } 

 <p id="timer">00:00</p> <button onclick="change()">My Button</button> 

Answer 4

Try with onchange attribute or maybe this one can help you:

Add event handler to HTML element using javascript