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JavaScript eval() function introduction and application examples_javascript skills

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WBOYOriginal
2016-05-16 16:40:521354browse

The

eval(String) function evaluates a string and executes the JavaScript code in it.

Return value

The value obtained by evaluating string (if any).

Description

This method only accepts raw strings as parameters. If the string parameter is not a raw string, then the method will return unchanged. Therefore please do not pass String objects as arguments to the eval() function.

ECMAScript implementations allow an EvalError exception to be thrown if an attempt is made to override the eval property or assign the eval() method to another property and call it through that property.

Throws

If there are no legal expressions and statements in the parameters, a SyntaxError exception will be thrown.

If eval() is called illegally, an EvalError exception will be thrown.

If the Javascript code passed to eval() generates an exception, eval() will pass the exception to the caller.

Tips and Notes

Tip: Although eval() is very powerful, it is rarely used in actual use.

Example: 

<html>
<body>

<script type="text/javascript">

eval("x=10;y=20;document.write(x*y)")
document.write("<br />")

document.write(eval("2+2"))
document.write("<br />")

var x=10
document.write(eval(x+17))
document.write("<br />")

eval("alert('Hello world')")

</script>

</body>
</html>

Output:

200

4

24

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