jQuery的isNumeric疑惑

Question

贴上jQuery的源码    isNumeric: function( obj ) {        // As of jQuery 3.0, isNumeric is limited to        // strings and numbers (primitives or objects)        // that can be coerced to finite numbers (gh-2662)        var type = jQuery.type( obj );        return ( type === "number" || type === "string" ) &&            // parseFloat NaNs numeric-cast false positives ("")            // ...but misinterprets leading-number strings, particularly hex literals ("0x...")            // subtraction forces infinities to NaN            !isNaN( obj - parseFloat( obj ) );    },为什么需要obj - parseFloat( obj )而不是直接obj - obj是为了排除什么情况？在问题补充回答。空字符串的情况

Answer 1

 // ...but misinterprets leading-number strings, particularly hex literals ("0x...")

注释里已经写的很明白了啊