Function toNumber

vue.js:128–132

* Convert a input value to a number for persistence. * If the conversion fails, return original string.

(val)

     * If the conversion fails, return original string.
     */
    function toNumber(val) {
        //字符串转数字，如果失败则返回字符串
        var n = parseFloat(val);
        return isNaN(n) ? val : n
    }

    /**
     * Make a map and return a function for checking if a key