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javascriptnumbers

Why does Number constructor fail to parse numbers with separators?

Since JavaScript has numeric separators (_, U+005F), why does Number("3_0") return NaN? Shouldn't it work like Number("0x08") which returns 8?

Number.isNaN(Number("3_0")) // true
Number.isNaN(Number(3_0))   // false
Number("3_0") === 30        // false
Number(3_0) === 30          // true
Solution

  • According to the spec, there are a few differences between the syntax accepted for numeric literals and the syntax accepted for a string value when being converted to a numeric value.

    One of the differences is

    A StringNumericLiteral cannot include a NumericLiteralSeparator.

    If I have to guess, the reason is that accepting such characters would change the behavior of existing valid JavaScript code, which may break working applications.