HTML DOM

HTML DOM console warn() Method

The console.warn() method outputs a warning message to the web console. Browsers display these messages with a yellow background and a warning icon, so they stand out from ordinary log entries.

Definition and Usage

console.warn() prints one or more values to the browser's console as a warning. It does not stop your code; it simply highlights something the developer should notice, such as a deprecated feature or an unexpected but non-fatal condition.

It accepts the same arguments as console.log() - strings, numbers, objects, and format specifiers like %s or %d. The only difference is the yellow warning styling the browser applies.

Syntax

console.warn(message)

Example

Open the developer console (F12) and run this snippet. The message appears with a yellow warning highlight.

Log a simple warning

console.warn("This feature is deprecated.");
console.warn("Loaded %d items, expected %d", 8, 10);

More Examples

Warnings are useful for guarding against risky input without breaking the page.

Warn on unexpected input

function setAge(age) {
  if (age < 0) {
    console.warn("Age should not be negative:", age);
    age = 0;
  }
  return age;
}
setAge(-5);

💡

Use console.warn() for problems that are recoverable and console.error() for genuine failures. Reserving each for its purpose keeps the console readable.

Key Takeaways

console.warn() logs a warning message to the console.
It does not stop script execution.
Browsers style the output in yellow with a warning icon.
Use it for recoverable issues, not fatal errors.