数字开头的Javascript 0 [英] Javascript 0 in beginning of number

问题描述

我只想在数字的开头用0-s理解js逻辑。
例如

I just want to understand js logic with 0-s in beginning of number. For example

var x = 09.3
// here x == 9.3
// other example
09.3 == 9.3
// returns true

// but check this one
var x = 02.5
// Uncaught SyntaxError: Unexpected number
// or this one
02.5 == 2.5 
// same error here

任何人都可以解释，它是如何工作的，为什么在第一个例子中它起作用，并忽略前导零，但在第二个例子中它给了我一个SyntaxError

Can anyone explain, how it works, why in first example it works, and ignores leading zeros, but in second example it gives me a SyntaxError

谢谢

推荐答案

数字文字中的前导 0 表示八进制整数是意图，除非 第二个数字是 8 或 9 。在这种情况下，前导 0 将被忽略。

Leading 0 on a numerical literal indicates that an octal integer is the intention, unless the second digit is 8 or 9. In that case, the leading 0 is ignored.

因为八进制数字文字必须是整数， 02.5 是错误的。

Because octal numeric literals must be integers, 02.5 is erroneous.

此行为在2014年被记录为Firefox中的一个错误，但因为世界上有如此多的JavaScript代码而且很多（可能是无意中）依赖 09.3 不是语法错误，错误标记为WONTFIX。

This behavior was logged as a bug in Firefox in 2014, but because there's so much JavaScript code in the world and so much of it (probably inadvertently) relies on 09.3 not being a syntax error, the bug was marked "WONTFIX".

正如下面的评论所指出的那样，在严格模式下，完全不允许八进制常量。

As pointed out in a comment below, in "strict" mode octal constants are disallowed entirely.

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