/** * Check if a string starts with $ or _ */ function isReserved (str) { var c = (str + '').charCodeAt(0); return c === 0x24 || c === 0x5F }
确保任意类型变量都可以拿到其字符串形式的第一个字符的码点,确保任意类型变量都不会报错说
Uncaught TypeError: str.charCodeAt is not a function
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