console: assert() method
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
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)
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.
Return value
None (undefined
).
Examples
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.
Specifications
Specification |
---|
Console Standard # assert |
Browser compatibility
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