JavaScript has a built in error object that provides error information when an error occurs.
The error object provides two useful properties: name and message.
Error Object Properties
| Property | Description |
|---|---|
| name | Sets or returns an error name |
| message | Sets or returns an error message (a string) |
Error Name Values
Six different values can be returned by the error name property:
| Error Name | Description |
|---|---|
| EvalError | An error has occurred in the eval() function |
| RangeError | A number "out of range" has occurred |
| ReferenceError | An illegal reference has occurred |
| SyntaxError | A syntax error has occurred |
| TypeError | A type error has occurred |
| URIError | An error in encodeURI() has occurred |
The six different values are described below.
Eval Error
An EvalError indicates an error in the eval() function.
Newer versions of JavaScript do not throw EvalError. Use SyntaxError instead.
Range Error
A RangeError is thrown if you use a number that is outside the range of legal values.
For example: You cannot set the number of significant digits of a number to 500.
Example
try {
num.toPrecision(500); // A number cannot have 500 significant digits
}
catch(err) {
document.getElementById("demo").innerHTML = err.name;
}
Reference Error
A ReferenceError is thrown if you use (reference) a variable that has not been declared:
Example
try {
x = y + 1; // y cannot be referenced (used)
}
catch(err) {
document.getElementById("demo").innerHTML = err.name;
}
Syntax Error
A SyntaxError is thrown if you try to evaluate code with a syntax error.
Example
eval("alert('Hello)"); // Missing ' will produce an error
}
catch(err) {
document.getElementById("demo").innerHTML = err.name;
}
Type Error
A TypeError is thrown if you use a value that is outside the range of expected types:
Example
try {
num.toUpperCase(); // You cannot convert a number to upper case
}
catch(err) {
document.getElementById("demo").innerHTML = err.name;
}
URI (Uniform Resource Identifier) Error
A URIError is thrown if you use illegal characters in a URI function:
Example
decodeURI("%%%"); // You cannot URI decode percent signs
}
catch(err) {
document.getElementById("demo").innerHTML = err.name;
}
Non-Standard Error Object Properties
Mozilla and Microsoft defines some non-standard error object properties:
lineNumber (Mozilla)
columnNumber (Mozilla)
stack (Mozilla)
description (Microsoft)
number (Microsoft)
Do not use these properties in public web sites. They will not work in all browsers.
Practice Excercise Practice now