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COMPUTER SOFTWARE APPLICATION - CITS

JavaScript Errors

Throw, and Try...Catch...Finally
The try statement defines a code block to run (to try).

The catch statement defines a code block to handle any error.
The finally statement defines a code block to run regardless of the result.
The throw statement defines a custom error.
Errors Will Happen!
When executing JavaScript code, different errors can occur.
Errors can be coding errors made by the programmer, errors due to wrong input, and other unforeseeable things.

Example
In this example we misspelled “alert” as “adddlert” to deliberately produce an error:
<p id=”demo”></p>
<script>

try {
adddlert(“Welcome guest!”);
}
catch(err) {
document.getElementById(“demo”).innerHTML = err.message;

}
</script>
JavaScript catches add alert as an error, and executes the catch code to handle it.
JavaScript try and catch
The try statement allows you to define a block of code to be tested for errors while it is being executed.

The catch statement allows you to define a block of code to be executed, if an error occurs in the try block.
The JavaScript statements try and catch come in pairs:
try {
Block of code to try
}

catch(err) {
Block of code to handle errors
}
JavaScript Throws Errors

When an error occurs, JavaScript will normally stop and generate an error message.
The technical term for this is: JavaScript will throw an exception (throw an error).
JavaScript will actually create an Error object with two properties: name and message.
The throw Statement
The throw statement allows you to create a custom error.
Technically you can throw an exception (throw an error).

The exception can be a JavaScript String, a Number, a Boolean or an Object:
throw “Too big”; // throw a text

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CITS : IT&ITES - Computer Software Application - Lesson 37 - 46