英語 での Instanceof の使用例とその 日本語 への翻訳
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If(err instanceof SyntaxError){.
Is null check needed before calling instanceof?
BC: instanceof will always return trueDodgy code.
So the outer code checks instanceof ReadError and that's it.
We can use it as an extended typeof and an alternative for instanceof.
We also can use instanceof to check the inheritance:.
A side effect of such call is that you canuse xpcomInterface's properties on obj after a successful instanceof test.
We can use instanceof to check for particular errors.
But if we inherit,then it becomes possible to use obj instanceof Error to identify error objects.
Conveniently, x instanceof Y does exactly this kind of search.
For example, if you need to report different types of exceptions in different ways,you may use the PHP instanceof comparison operator:.
We talk about classes, new, instanceof, prototype chains, and API design.
This instanceof test will always return true(unless the value being tested is null).
The mock object will pass type hints or instanceof evaluations for the existing class.
And instanceof check will continue to work for new inheriting classes. So that's future-proof.
Please take a look at how we use instanceof to check for the specific error type in the line(*).
The instanceof OperatorThe instanceof operator compares the constructors of its two operands.
There were some issueswith the initial implementation of instanceof, which relied on__autoload() to search for missing classes.
But instanceof does not care about the function, but rather about its prototype, that it matches against the prototype chain.
For example, if you need to report different types of exceptions in different ways,you may use the PHP instanceof comparison operator:.
So, by the logic of instanceof, the prototype actually defines the type, not the constructor function.
This change should not affect your code unless it checks for the object type for some reason, like below:error instanceof DOMError.
Instead of making a lot of instanceof checks in your report method, consider using reportable exceptions.
XPConnect knows all about tearoffs and modifies the object that you QueryInterface or instanceof to cache all its known interfaces.
And instanceof operator really shines when we are working with a class hierarchy and want to check for the class taking into account inheritance.
Unlike standard JavaScript globals, the test obj instanceof xpcomInterface works as expected even if obj is from a different scope.
The instanceof version is much better, because in the future we are going to extend ValidationError, make subtypes of it, like PropertyRequiredError.
This offers all the usual mock object goodness but the resulting mock will not inherit the class type of the object being mocked,i.e. it will not pass any instanceof comparison.
In modern scripts, we can use instanceof and other class-based tests to see the node type, but sometimes nodeType may be simpler.
One caveat to the instanceof solution is that it doesn't work when there are multiple copies of React on the page, and the component we're checking inherits from another React copy's React. Component.