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1 Functions

Functions

To define functions we have the instruction function

After this reserved word is placed the name of the function followed by a list of arguments delimited by parentheses and separated by commas

function name (param1, param2, ..., paramN) {
    JavaScript instructions;
}

The return statement

The statement return it is the one that allows you to return the result of a function

function Area(l) {
    return l * l;
}

The example shows a function that returns the area of a square of side l

Properties of the functions

JavaScript associates two properties with each function:

arguments
it allows the management of the optional parameters
caller
identifies the function that made the call

The property arguments

Is an array that contains the parameters that are passed to the function

function Sum(x) {
    var summand = Sum.arguments;
    var num_op = Sum.arguments.length;
    var result = 0;
    for (var i=0; i<num_op; i++) {
        result += summands[i];
    }
    return result;
}

In the example we have defined the Sum function to calculate the sum of the numbers passed as arguments

Thus, Sum(4,5,7) returns 16 and Sum(56) returns 56

The caller property

Displays the name of the calling function, so this property will return a string of characters

Considerations to be taken into account

Before you start working with features, you need to consider the following points:

The JavaScript language does not allow the definitions of nested functions
The passing of parameters is done by value

That is, if a function modifies the content of its arguments, this modification is local and does not affect either globally or the function made the call

Functions are predefined by the language

Eval function

Has as argument an expression and returns the value of the same

This function is useful to evaluate a string of characters that represents a numeric expression

The issue was effected through a form field is a string of characters that it is sometimes necessary to convert to a numeric value

<script type="text/javascript">
function calculated(obj) {
    obj.result.value = eval(obj.expr.value);
}
</script>

<center><form name="evalua">
    <table border="1" style="font-size: 10px;">
        <tr>
            <td><label for="expr"><strong>Enter expression:</label><input type="text" name="expr" size=20 value="0" /></td>
            <td><label for="result"><strong>Result:</label><input type="text" name="result" size=20 /></td>
    </table>
    <input type="button" value="evaluate" onclick="calculated(this.form)"></input>
</form></center>

The following example illustrates how allowing the user to enter a numeric expression you can visualize it as the value of the expression

If you haven't entered anything, you see undefined and if it's not a numerical expression, it doesn't make changes to the visualization

Functions escape and unescape

These two functions allow you to encode strings in URL format

This encoding is necessary in the automatic creation of hypertext links or in the definition of persistent properties as the Cookies

<script type="text/javascript">
    escape("#"); // return %23
    unescape("%23"); // return #
</script>

<center><form name="escape_unescape">
    <table border="1" style="font-size: 7.5px;">
        <tr>
          <td><label for="char">Enter the text in URL or normal format:</label><input name="char" type="text" value="%23" size="5" /></td>
        </tr>
        <tr>
             <td><input name="codificacion" type="radio" onclick="this.form.char.value=escape(this.form.char.value)" value="normal" checked="checked"></input><label for="codificacion">standard URL format</label></td>
        </tr>
        <tr>
             <td><input type="radio" name="codificacion" value="URL" onclick="this.form.char.value=unescape(this.form.char.value)"></input><label for="codificacion">URL format to standard</label></td>
        </tr>
     </table>
</form></center>

Function isNaN

Function that checks if the value passed for the parameter is numeric or not

The result of this function is a Boolean

That is, it evaluates an argument to see if it is NaN: (Not a Number)

<script type="text/javascript">
//isNaN(input value)

function Check(form) {
    var number = parseFloat(form.valor.value);
    if (isNaN(number)==true) {
        alert("Not a number");
    }else{
        alert("It is a number");
    }
}
</script>

<center><form name="isNaN">
    <table border="1" style="font-size: 10px;">
        <tr>
            <td><label for="value"><strong>Enter a numeric value:</strong></label><input type="text" name="value" value="0" /></td>   
        </tr>
     </table>
     <input type="button" value="Check" onClick="Check(this.form)"></input>
</form></center>

Function parseFloat

Converts a string of characters to a floating-point number

If a non number character is found, the sign '+', '-' or exponent, returns the value found up to that point

Similarly, if the first character cannot be converted to number it will return zero

<script type="text/javascript">
    //parseFloat(string)
</script>

<center><form name="real">
    <table border="1" style="font-size: 10px;">
        <tr>
            <td><label for="float"><strong>Makes real:</strong></label><input type="text" name="float" value="0.0" /></td>
        </tr>
     </table>
     <input type="button" value="Converts" onclick="this.form.float.value=parseFloat(this.form.float.value)"></input>
</form></center>

Function parseInt

Converts a string of characters to an integer number with a specified base

La base puede ser 8, 10 ó 16

If a non number character is found, the sign '+', '-' or exponent, returns the value found up to that point

Similarly, if the first character cannot be converted to number it will return zero

<script type="text/javascript">
//parseInt (string, base) base is optional

function makes(obj, base) {
    obj.valor.value = parseInt(obj.int.value, base);
}
</script>

<center><form name="integer">
    <table border="1" style="font-size: 10px;">
        <tr>
            <td><label for="int"><strong>Enter integer:</strong></label><input type="text" name="int" value="15" /></td>   
            <td><label for="value"><strong>Result:</strong></label><input type="text" name="value" /></td>    
        </tr>
        <tr>
             <td><input type="radio" name="convert" value="decimal" onclick="convierte(this.form, 10)" /><label for="convert">Express decimal integer<label/></td>
        </tr>
        <tr>
             <td><input type="radio" name="convert" value="hexadecimal" onclick="convierte(this.form, 16)" /><label for="convert">Express integer in hexadecimal</label></td>
        </tr>
        <tr>
             <td><input type="radio" name="convert" value="octal" onclick="convierte(this.form, 8)" /><label for="convert">Express integer in octal</label></td>
        </tr>
     </table>
</form></center>

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Secarcam's Computer Science Web

Functions in Javascript

Functions

The return statement

Properties of the functions

The property arguments

The caller property

Considerations to be taken into account

Functions are predefined by the language

Eval function

Functions escape and unescape

Function isNaN

Function parseFloat

Function parseInt

Web page of Sergio Cárcamo Garcia dedicated to the computing and related topics such as programming languages, statistics, mathematics, etc

Enter integer:	Result:
Express decimal integer
Express integer in hexadecimal
Express integer in octal

Functions

The return statement

Properties of the functions

The property arguments

The caller property

Considerations to be taken into account

Functions are predefined by the language

Eval function

Functions escape and unescape

Function isNaN

Function parseFloat

Function parseInt

Web page of Sergio Cárcamo Garcia dedicated to the computing and related topics such as programming languages, statistics, mathematics, etc

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