How does jquery determine whether a certain attribute exists hasAttr

Jquery method to determine whether hasAttr exists for an attribute: Use [if(typeof($("#aid").attr("rel"))=="undefined")] to determine whether it exists A certain attribute [$("#aid").attr("rel")] will return the value of rel.

The operating environment of this tutorial: windows7 system, jquery3.2.1 version. This method is suitable for all brands of computers.

Jquery's method of determining whether an attribute exists hasAttr:

In JQuery coding, we will determine whether an element exists or not. For example, whether it contains class=" new" style. JQuery judgment is very simple,

because there is the hasClass method $("input[name=new]").hasClass("new") That's it Judgment.

But sometimes we need to judge other attributes. For example, some a links contain the rel attribute, and some do not. How to judge at this time?

There is no such thing at this time A ready-made method. If there is an attribute $("#aid").attr("rel"), the value of rel will be returned. If the rel attribute does not exist, "undefined"

will be returned.

undefined is the undefined type, if($("#aid").attr("rel")=="undefined") This judgment may not be true.

Because the type is not Same.

It is recommended to useif(typeof($("#aid").attr("rel"))=="undefined") That's it

Related learning recommendations: javascript video tutorial

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