shows a message. An if statement will evaluate whether a statement is true or false, and only run if the statement returns true. Let’s recall the conversion rules from the chapter Type Conversions: So, the code under this condition would never execute: …and inside this condition – it always will: We can also pass a pre-evaluated boolean value to if, like this: The if statement may contain an optional “else” block. Confirmation Dialog Box. A Computer Science portal for geeks. Where to define it? JavaScript provides different built-in functions to display popup messages for different purposes e.g. We can use the else statement with if statement to execute a block of code when the condition is false. prompt shows a message asking the user to input text. Awarded Oracle ACE award in October 2020, from the Oracle corporation for my contribution to Oracle communities. Technically, we can omit the parentheses around age > 18. A software consultant by profession and blogger by hobby. This guide will show you how to diagnose JavaScript issues in different browsers. JavaScript has three kind of popup boxes: Alert box, Confirm box, and Prompt box. The difference becomes obvious when we look at the code inside a function. As earlier we have discussed JavaScript Message box used to show pop up messages, also if we want to notify user for specific messages or warning it possible to show. JavaScript: all type Message Box. Javascript alert box messages - alert your users to important messages. The conditional expression 1 > 0 will be evaluated to true, so an alert message "1 is greater than 0" will be displayed, whereas conditional expression in second if statement will be evaluated to false, so "1 is less than 0" alert message will not be displayed. Also see the HTML