Javascript console.assert() Method

Introduction

Write a message to the console, only if the first argument is false: 

console.assert(document.getElementById("demo"), "You have no element with ID 'demo'");

View in separate window 

<!DOCTYPE html>
<html>
<body>
<script>
console.assert(document.getElementById("demo"), "You have no element with ID 'demo'");
</script>/*from  ww w  .  ja  v a2 s  . c o  m*/
</body>
</html>

The console.assert() method writes a message to the console, only if an expression evaluates to false. 

console.assert(expression, message);

Parameter Values

Parameter Type Description
expression A Boolean expression Required. If the expression evaluates to false, the message is written in the console
messageString or Object Required. The message or object to write in the console



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