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assert method

Sends a message to the console if the expression provided evaluates to false. The message text color is red and it is prefaced by an error icon.



Console.assert(test, message, optionalParams);


  • test [in]
    Type: boolean

    An expression that if false, will cause an assert message to be sent. True results, no message is sent.

  • message [in]
    Type: DOMString

    The message to display.

  • optionalParams [in]
    Type: any

    A value or string that can be used with replaceable parameters in the main message.

Return value

This method does not return a value.


The optional parameters can be used to provide a replaceable value in the message. For example, you could include a specific message or value as the optional parameter, rather than building a string by concatenating the value to the message string.

  function sendAssertConsole(cmpValue) {
        window.console.assert( (cmpValue > 3), "%s is too small", cmpValue);

See also