identity-operator | 易学教程

What is the difference between == and === in JavaScript? [duplicate]

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问题 This question already has answers here : Closed 9 years ago . Possible Duplicate: Javascript === vs == : Does it matter which “equal” operator I use? When would JavaScript == make more sense than ===? What is the difference between below methods in comparing a string with undefined value. var x; if(x==undefined) { alert(x); } and if(x===undefined) { alert(x); } Why should i prefer second method in this case.. Please let me know advantages.. 回答1: == attempts to convert the values to the same

What is the difference between == and === in JavaScript? [duplicate]

阅读更多关于 What is the difference between == and === in JavaScript? [duplicate]

What is the difference between == and === in JavaScript? [duplicate]

阅读更多关于 What is the difference between == and === in JavaScript? [duplicate]

How do I achieve the effect of the === operator in Python?

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问题 How do I achieve the effect of the === operator in Python? For example, I don't want False == 0 to be True . 回答1: Try variable is False . False is 0 returns False , 回答2: If you want to check that the value and type are the same use: x == y and type(x) == type(y) In Python, explicit type comparisons like this are usually avoided, but because booleans are a subclass of integers it's the only choice here. x is y compares identity—whether two names refer to the same object in memory. The Python

When would JavaScript == make more sense than ===?

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问题 As Which equals operator (== vs ===) should be used in JavaScript comparisons? indicates they are basically identical except ' === ' also ensures type equality and hence ' == ' might perform type conversion. In Douglas Crockford's JavaScript: The Good Parts , it is advised to always avoid ' == '. However, I'm wondering what the original thought of designing two set of equality operators was. Have you seen any situation that using ' == ' actually is more suitable than using ' === '? 回答1:

Why is === faster than == in PHP?

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问题 Why is === faster than == in PHP? 回答1: Because the equality operator == coerces, or converts, the data type temporarily to see if it’s equal to the other operand, whereas === (the identity operator) doesn’t need to do any converting whatsoever and thus less work is done, which makes it faster. 回答2: === does not perform typecasting, so 0 == '0' evaluates to true , but 0 === '0' - to false . 回答3: First, === checks to see if the two arguments are the same type - so the number 1 and the string '1

How do the PHP equality (== double equals) and identity (=== triple equals) comparison operators differ?

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问题 What is the difference between == and === ? How exactly does the loosely == comparison work? How exactly does the strict === comparison work? What would be some useful examples? 回答1: Difference between == and === The difference between the loosely == equal operator and the strict === identical operator is exactly explained in the manual: Comparison Operators ┌──────────┬───────────┬───────────────────────────────────────────────────────────┐ │ Example │ Name │ Result │ ├──────────┼───────────

When would JavaScript == make more sense than ===?

阅读更多关于 When would JavaScript == make more sense than ===?

As Which equals operator (== vs ===) should be used in JavaScript comparisons? indicates they are basically identical except ' === ' also ensures type equality and hence ' == ' might perform type conversion. In Douglas Crockford's JavaScript: The Good Parts , it is advised to always avoid ' == '. However, I'm wondering what the original thought of designing two set of equality operators was. Have you seen any situation that using ' == ' actually is more suitable than using ' === '? Consider a situation when you compare numbers or strings: if (4 === 4) { // true } but if (4 == "4") { // true }

Why does new String('hello') === new String('hello') evaluate to False? [duplicate]

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This question already has an answer here: Which equals operator (== vs ===) should be used in JavaScript comparisons? 49 answers JavaScript comparison operators: Identity vs. Equality 4 answers Why does the following statement return false in JavaScript? new String('hello') === new String('hello') Pointy Two String objects will always be unequal to each other. Note that JavaScript has string primitive values as well as a String constructor to create wrapper objects. All object equality comparisons (especially with === ) are carried out as a test for reference equality . References to two

id() vs `is` operator. Is it safe to compare `id`s? Does the same `id` mean the same object?

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How much can I rely on the object's id() and its uniqueness in practice? E.g.: Does id(a) == id(b) mean a is b or vice versa? What about the opposite? How safe is it to save an id somewhere to be used later (e.g. into some registry instead of the object itself)? (Written as a proposed canonical in response to Canonicals for Python: are objects with the same id() the same object, `is` operator, unbound method objects ) According to the id() documentation , an id is only guaranteed to be unique for the lifetime of the specific object, and within a specific interpreter instance As such, comparing