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
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
js
assert(assertion, obj1) assert(assertion, obj1, obj2) assert(assertion, obj1, obj2, /* …, */ objN) assert(assertion, msg) assert(assertion, msg, subst1) assert(assertion, msg, subst1, /* …, */ substN)
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.
None (undefined
).
The following code example demonstrates the use of a JavaScript object following the assertion:
js
const errorMsg = "the # is not even"; for (let number = 2; number <= 5; number++) { console.log(`the # is ${number}`); console.assert(number % 2 === 0, "%o", { 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 Using string substitutions in the documentation of console
for further details.
Specification |
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Console Standard # assert |
Desktop | Mobile | |||||||||||
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Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | |
assert |
2 | 12 | 28 | 8 | 11 | 4 | ≤37 | 18 | 28 | 11 | 3.2 | 1.0 |
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https://developer.mozilla.org/en-US/docs/Web/API/console/assert