console.assert()
The console.assert()
method writes an error message to
the console if the assertion is false. If the assertion is true, nothing happens.
Note: This feature is available in Web Workers
Syntax
console.assert(assertion, obj1 [, obj2, ..., objN]);
console.assert(assertion, msg [, subst1, ..., substN]); // C-like message formatting
Parameters
assertion
-
Any boolean expression. If the assertion is false, the message is written to the console.
obj1
...objN
-
A list of JavaScript objects to output. The string representations of each of these objects are appended together in the order listed and output.
msg
-
A JavaScript string containing zero or more substitution strings.
subst1
...substN
-
JavaScript objects with which to replace substitution strings within
msg
. This parameter gives you additional control over the format of the output.
Examples
The following code example demonstrates the use of a JavaScript object following the assertion:
const errorMsg = 'the # is not even';
for (let number = 2; number <= 5; number += 1) {
console.log('the # is ' + number);
console.assert(number % 2 === 0, {number: number, errorMsg: errorMsg});
// or, using ES2015 object property shorthand:
// console.assert(number % 2 === 0, {number, errorMsg});
}
// output:
// the # is 2
// the # is 3
// Assertion failed: {number: 3, errorMsg: "the # is not even"}
// the # is 4
// the # is 5
// Assertion failed: {number: 5, errorMsg: "the # is not even"}
See Outputting
text to the console in the documentation of console
for further
details.
Specifications
Specification |
---|
Console Standard # assert |
Browser compatibility
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