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How to Execute Script After Specific Delay Using JavaScript and Prevent Variable Value Changes?

Oct 31, 2024 pm 10:38 PM

How to Execute Script After Specific Delay Using JavaScript and Prevent Variable Value Changes?

Execute Script After Specific Delay Using JavaScript

When seeking a JavaScript method analogous to jQuery's "delay()" or "wait()" functions, which allow for delayed script execution, "setTimeout()" emerged as a reliable solution.

However, when it comes to invoking a function with a parameter at a later time, anonymous function calls must be utilized.

While it's tempting to pass a function as an argument for later invocation by omitting the brackets after its name, this approach has a caveat:

var a = "world";
setTimeout(alert("Hello" + a), 2000); // Displays "Hello world" immediately
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To ensure delayed execution, either use a function name (as demonstrated by Flubba) or an anonymous function, particularly when passing a parameter:

var a = "world";
setTimeout(function() { alert("Hello" + a); }, 2000); // Displays "Hello world" after 2 seconds
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However, this alternative has a limitation: variables may change during the delay, altering the function's output. To preserve the original variable value, employ a callback function:

function callback(a) {
  return function() {
    alert("Hello" + a);
  }
}
var a = "world";
setTimeout(callback(a), 2000);
a = "Stack Overflow"; // This change won't affect the delayed function
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By embodying the original variable value within the callback function, it ensures that the delayed invocation occurs with the intended value, even if it has changed in the meantime.

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