Javascript forms and validation-non-null validation_javascript skills

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JavaScript can be used to validate input data in HTML forms before the data is sent to the server.

Check the legality of the data before submitting the form

When you want to verify the data in the form, you can use getElementById() to access any element on the web page

Each form field has a form object that can be passed to any function that validates form data

<input id="zipcode" name="zipcode" type="text" size="5" onclick="showIt(this.form)"/>
function showIt(thisForm)
{
alert(thisForm["zipcode"].value);
//通过form对象的name属性，取得元素的值
}

You can use the name attribute or getElementById() method to obtain the element

The timing of checking form data depends on choosing the correct user input event to handle.

In other words, the data is verified immediately after the user enters the data.

The order in which users enter data is:

Select input field

Enter data in the field

Leave this area and move to the next target

Select next target domain

Enter data in the field

In this process, a series of events will be triggered. Using these events, you can find the opportunity to verify the data

1) When the input field is selected – the onfocus event (focus) is fired

2) When leaving the input field – fire onblur event (leaving focus)

3) When you leave the domain and the input content changes – fire the onchange event

The most correct choice is to verify the data when the onblur event is fired

The first step of verification: check that the domain is not empty

<input id="phone" name="phone" type="text" size="12" onblur="validateNonEmpty(this)"/>

Call validateNonEmpty to respond to the onblur event

The form object is passed to the function using the keyword this

The following is the verification function

function validateNonEmpty(inputField)
{
if(inputField.value.length==0)
{
alert("Please enter a value.");
return false;
} 
return true;
}

When submitting a web form, the data entered by the user must be verified

When you want to verify the data in the form, you can use getElementById() to access any element on the web page

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