How to speed up your JavaScript code.
Loops are often used in programming.
Every statement inside a loop will be executed for each iteration of the loop.
Search for statements or assignments that can be placed outside the loop.
Accessing the HTML DOM is very slow, compared to other JavaScript statements.
If you expect to access a DOM element several times, access it once, and use it as a local variable:
Keep the number of elements in the HTML DOM small.
This will always improve page loading, and speed up rendering (page display), especially on smaller devices.
Every attempt to search the DOM (like getElementsByTagName) will benefit from a smaller DOM.
Don't create new variables if you don't plan to save values.
Often you can replace code like this:
With this:
Putting your scripts at the bottom of the page body, lets the browser load the page first.
While a script is downloading, the browser will not start any other downloads. In addition all parsing and rendering activity might be blocked.
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The HTTP specification defines that browsers should not download more than two components in parallel. |
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An alternative is to use defer="true" in the script tag. The defer attribute specifies that the script should be executed before the page has finished parsing, but it only works for external scripts.
If possible, you can add your script to the page by code, after the page has loaded:
Avoid using the with keyword. It has a negative effect on speed. It also clutters up JavaScript scopes.
The with keyword is not allowed in strict mode.
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