VirtualMV/JavaScript/Calculations/Home
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< VirtualMV | JavaScript
Simple Math calculations
<html> <head><title>JavaScript Math (increase/decrease variable)</title></head> <body> <script type="text/javascript"> var intX; intX = 2; intX += 3; document.write( intX + ", "); //Adds 3 to intX intX -= 2; document.write( intX ); //Subtracts 2 from intX</script> </body> </html>
Math object
The built-in Math object includes mathematical constants and functions. You do not need to create the Math object before using it.
| function | Meaning (returns ..) |
| abs(x) | the absolute value of x |
| ceil(x) | the nearest integer greater than or equal to x |
| cos(x) | the cosine of x |
| exp(x) | the value of E raised to the power of x |
| floor(x) | the nearest integer less than or equal to x |
| log(x) | natural log of x |
| max(x,y) | the number with the highest value of x and y |
| min(x,y) | the number with the lowest value of x and y |
| pow(x,y) | the value of the number x raised to the power of y |
| random() | a random number between 0 and 1 |
| round(x) | x rounded to the nearest integer |
| sin(x) | the sine of x |
| sqrt(x) | the square root of x |
| tan(x) | the tangent of x |
Math example 1 (js6_01)
<html> <head><title>JavaScript Math (js6_01)</title></head> <body> <script type="text/javascript"> document.write("Maximum of 2 & 4 is " +Math.max(2,4)+ "<br />") document.write("Mimimum of 2 & 4 is " +Math.min(2,4) + "<br />") document.write("Rounded value of 7.25 is " +Math.round(7.25) + "<br />") vntNum=Math.random()*10 document.write("Random number between 0 and 9 is " +Math.floor(vntNum) + "<br />")</script> </body> </html>
Note:Use refresh to see the random number change.
Example js6_01
Math example 2 Currency converter (js6_02)
<html> <head> <title>Currency Formatter</title> <script type="text/javascript"> function fnCurrencyconv(vntAmount) { vntAmount=parseFloat(vntAmount); // find number (parseFloat) vntAmount=vntAmount*100; //convert to cents vntAmount=Math.floor(vntAmount); //chop of any decimals (floor) vntAmount=vntAmount/100; //convert to dollars and cents document.frmConvert.txtCurrency.value= "$" + vntAmount } </script> </head> <body> <form name="frmConvert"> Enter a number with lots of decimals: <input name="txtAmount" type="text" value="" onChange="fnCurrencyconv(this.value)" /><br /> Currency value: <input name="txtCurrency" type="text" value="" /> </form> </body> </html>
Notes:
- ParseFloat: Determines if the first character in the specified string is a number. If it is, it parses the string until it reaches the end of the number, and returns the number as a number, not as a string.
- this.value is shorthand that says use "this" objects value
- You need to click "off" the number for the currency to be shown.
Example js6_02
Currency conversion:
An easier solution was made available with JavaScript 1.5
$numin.toFixed(x) e.g.
var vntNum = new Number(13.378); document.write (vntNum.toFixed(2)); // two decimal places
parseFloat
An issue that arises is when a number is expected in a textBox but the user does not enter one. In this case parseFloat will return Not a Number (NaN) and the arithmetic will not evaluate.
This can be fixed by adding an if statement straight after the number is converted, for example:
vntNum = parseFloat(document.getElementById("txtNum").value); if (isNaN(vntNum)){vntNum = 0; }
This example shows the results of different JavaScript code Example js6_03
Activity: Simple calculator
- Create two text boxes (number 1 and Number 2) and four buttons +,*,*,/ plus an Answer text box
- When a user enters two numbers they can click the appropriate button and the total is placed in the total box
.. add your code in here ...
References
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virtualMV | Superquick wiki guide | Please give me some feedback |
VirtualMV/JavaScript/Calculations/Home. (2024). In WikiEducator/VirtualMV wiki. Retrieved April 26, 2024, from http:https://wikieducator.org/VirtualMV/JavaScript/Calculations/Home (zotero)
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