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JavaScript Tutorial >> JavaScript Functions.

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Many web developers enjoy using VBScript, due to its many nice, inherent functions. However, Internet Explorer is the only browser which supports VBScript, so for production of web applications it is essential that all client-side scripting be written in JavaScript only.

What Is a JavaScript Function?

Microsoft JavaScript functions perform actions. JavaScript Functions can also return results. Sometimes these are the results of calculations or comparisons like mathematical operations.
JavaScript Functions combine several operations under one name. This lets us streamline our JavaScript code. We can write out a set of JavaScript statements, name it, and then execute the entire set any time we want to, just by calling it and passing to it any information it needs.

No in JavaScript Tutorial we will learn that we pass information to a JavaScript Function by enclosing the information in parentheses after the name of the JavaScript Function. Pieces of information that are being passed to a JavaScript Function are called arguments or parameters of JavaScript Function. Some JavaScript Functions don't take any arguments at all, some functions take one argument; some take several. There are even functions for which the number of arguments depends on how we are using the JavaScript Function.

JavaScript supports two kinds of functions: those that are built into the language, and those we create ourself.

Built-in Functions in JavaScript

The JavaScript language includes several built-in functions. Some of them let us handle expressions and special characters, and convert strings to numeric values.
For example, escape() and unescape() are used to convert characters that have special meanings in HTML code, characters that we cannot just put directly into text. For example, the angle brackets, "<" and ">", delineate HTML tags.

The escape JavaScript Function takes as its argument any of these special characters, and returns the escape code for the character. Each escape code consists of a percent sign (%) followed by a two-digit number. The unescape() JavaScript Function is the exact inverse. It takes as its argument a string consisting of a percent sign and a two-digit number, and returns a character.

Another useful built-in JavaScript Function is eval(), which evaluates any valid mathematical expression that is presented in string form. The eval() function of JavaScript takes one argument, the expression to be evaluated.

Example of Built-in JavaScript Functions

var anExpression = "6 * 9 % 7";

var total = eval(anExpression); 

// Assigns the value 5 to the variable total.

var yetNewExpression = "6 * (9 % 7)";

total = eval(yetNewExpression) 

// Assigns the value 12 to the variable total.

var totality = eval("Well come at Global Guide Line JavaScript Tutorial."); 

// Generates an error.

Creating our own Functions in JavaScript

We can create our own JavaScript functions and use them where we need them. A JavaScript function definition consists of a function statement and a block of JavaScript statements.

The checkTripletFunction function in the following example takes as its arguments the lengths of the sides of a triangle, and calculates from them whether the triangle is a right triangle by checking whether the three numbers constitute a Pythagorean triplet. The square of the length of the hypotenuse of a right triangle is equal to the sum of the squares of the lengths of the other two sides. The checkTripletFunction function calls one of two other functions to make the actual test.

Notice the use of a very small number "epsilon" as a testing JavaScript variable in the floating-point version of the test. Because of uncertainties and roundoff errors in floating-point calculations, it is not practical to make a direct test of whether the square of the hypotenuse is equal to the sum of the squares of the other two sides unless all three values in question are known to be integers. Because a direct test is more accurate, the code in this JavaScript Function example determines whether it is appropriate and, if it is, uses it. Lets see the code here in JavaScript Tutorial.

Example of JavaScript Function

var epsilon = 0.0000000000001;  // Some very small number to test against.
var triplet = false;

function integerCheck(a, b, c)  {  // The test function for integers.
    if ( (a*a) == ((b*b) + (c*c)) )  {  // The test itself.
    triplet = true;
}  // End of the integer checking function.

function floatCheck(a, b, c)  {  // The test function for floating-point numbers.
var theCheck = ((a*a) - ((b*b) + (c*c)))  // Make the test number.
    // The test requires the absolute value, so invert theCheck if it's negative.
    if (theCheck < 0)  { 
    theCheck *= -1;
    if (epsilon > theCheck)  {  // If it's as close as that, it's pretty darn close!
    triplet = true;
}  // End of the floating-poing check function.

// The triplet checker. First, move the longest side to position "a".
function checkTripletFunction(a, b, c)  { 
var d = 0;  // Create a temporary holding bin.
    if (c > b)  {  // If c > b, swap them.em.
    d = c;
    c = b;
    b = d;
    }  // If not, ignore them.
    if (b > a)  {  // If b > a, swap them.
    d = b;
    b = a;
    a = d;
    }  // If not, ignore them.

// Side "a" is now the hypotenuse, if there is one.

    if (((a%1) == 0) && ((b%1) == 0) && ((c%1) == 0))  {  // Test all 3 values. Are they integers?
    integerCheck(a, b, c);  // If so, use the precise check.
        floatCheck(a, b, c);  // If not, get as close as is reasonably possible.le.
}<  // End of the triplet check JavaScript function.

// The next three statements assign sample values for testing purposes.
var sideA = 5;
var sideB = 5;
var sideC = Math.sqrt(50);

checkTripletFunction(sideA, sideB, sideC);  // Call the function. After the call, triplet contains the

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Examples of JavaScript Functions

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