本文探讨了null与undefined在JavaScript中的使用。两者都表示没有值的状态，但它们的使用场景有所不同。null常用于程序级的正常空值表示，而undefined则更多地表示系统级的未定义状态。文章还讲解了如何通过不同的等号运算符来区分这两者。
共同点:
1, [color=red]null[/color] and [color=red]undefined[/color] both indicate an absence of value.
2. Both are falsy values-----they behave like false when a boolean value is required.
3. Neither null or undefined have any properties or methods.
不同点:
1. The equality operator== considers them to be equal.
Use the strict equality operator === to distinguish them
2. You might consider undefined to represent a system-level, unexpected, or error-like absence of value.
Null to represent program-level, normal, or expected absence of value.
1, [color=red]null[/color] and [color=red]undefined[/color] both indicate an absence of value.
2. Both are falsy values-----they behave like false when a boolean value is required.
3. Neither null or undefined have any properties or methods.
不同点:
1. The equality operator== considers them to be equal.
Use the strict equality operator === to distinguish them
2. You might consider undefined to represent a system-level, unexpected, or error-like absence of value.
Null to represent program-level, normal, or expected absence of value.
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