Calculate Miles Per Gallon

Miles Driven:
Gallons of Gas Used:
Miles Per Gallon

Alert Method vs JavaScript Function

Alert is a method that displays a dialog box that contains the string that is passed to it within parenthesis along with an OK button. Alert boxes were invented during the first generation of the Internet and were the only way of showing a dynamic message to the user. Refresh your screen to observe that the MPG Alert Method suspends the browser until the user clicks OK. You know that the browser is waiting for a response because it will show a spinning wheel in the title tab of the page.

A developer's best practice is to use a Javascript Function as illustrated in the Calculate Miles Per Gallon function in the box to the left. This code is placed in the head section of this document and called from the body. In both the Alert and Function routines, an error message of NaN will appear if the user enters data that is Not a Number.

var today = new Date(); document.write("Current date: "); document.write(today.toDateString());

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Calculate Miles Per Gallon