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In this article, the editor introduces "how to constrain and verify DOM" in detail, the content is detailed, the steps are clear, and the details are handled properly. I hope this "how to constrain and verify DOM" article can help you solve your doubts.

Constraint verification DOM method

CheckValidity (): returns true if the data in the input element is legal, false otherwise.

SetCustomValidity ()

Sets the validationMessage attribute of the input element, which is used to customize the method for error messages.

When you set a custom prompt using setCustomValidity, validity.customError becomes true, and checkValidity always returns false. If you want to rejudge, you need to cancel the custom prompt as follows:

SetCustomValidity ('')

SetCustomValidity (null)

SetCustomValidity (undefined)

The following example returns an error message if the input information is illegal:

CheckValidity () method

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