使用正则表达式和 javascript 在字符串中获取精确匹配

Question

我试图从给定的字符串中获取精确匹配，然后处理该字符串。我有一个相当大的计算器程序，您可以在这里看到：http://www.marcusparsons.com/projects/calculator。主页上还没有任何内容，原始代码很长。

我们的目标是在计算器中实现一项功能，其中 Math 不必在 Math objects/methods 前加上前缀。在我添加一个允许用户使用 "acosh()" 方法（和实验方法）的函数之前，它一直运行良好，而不管它是否在他们的浏览器中实现（ehem...IE）。我运行遇到的问题是我现在的算法想要用 aMath.cosh()" 替换 "acosh" 因为它在 "acosh" 中看到 "cos"。

因此，当我将字符串 "acosh(1)+cos(pi/3)" 传递给它时，它会变成 "aMath.cosh(1)+cos(Math.PI/3)"。

编辑：上面的字符串应该是 "acosh(1)+Math.cos(Math.PI/3)"。

我是正则表达式的新手，我想这就是我的问题所在。

示例代码如下：http://jsfiddle.net/mparson8/2ej5n3u4/4/

var $mathKeywords = ["E", "LN2", "LN10", "LOG2E", "LOG10E", "PI", "SQRT1_2", "SQRT2", "abs", "acos", "asin", "asinh", "atan", "atan2", "atanh", "cbrt", "ceil", "clz32", "cos", "exp", "expm1", "floor", "fround", "hypot", "imul", "log1p", "log10", "log2", "max", "min", "pow", "random", "round", "sin", "sinh", "sqrt", "tan", "tanh", "trunc"];

var $resultVal = "acosh(1)+cos(PI/3)".toLowerCase();
try {
//Iterate over each Math object/method
$.each($mathKeywords, function (i, val) {
    //Convert val within array to a lower case form
    var $lowerKey = val.toLowerCase();
    //The regex pattern I came up with
    var pattern = new RegExp("(^|\W)" + $lowerKey + "($|\W)");
    //See if pattern gives a match within $resultVal
    var $location = $resultVal.match(pattern);
    //Math keyword is found
    if ($location != null) {
        //replace the lowercase version of the math keyword with its properly cased version prepended 
        //with Math. i.e. cos becomes Math.cos and pi becomes Math.PI
        $resultVal = $resultVal.replace($lowerKey, "Math." + val);
    }
});
//Set the result element's value to an evaluation of $resultVal
//A better implementation of the eval exists within the calc program
alert($resultVal);
alert(eval($resultVal));
} catch (err) {
alert("Error: Cannot process expression due to " + err + ".");
}

感谢所有帮助！ :)

Answer 1

如果你想继续正则表达式的路径，这似乎可行：

var $mathKeywords = ["E", "LN2", "LN10", "LOG2E", "LOG10E", "PI", "SQRT1_2", "SQRT2", "abs", "acos", "asin", "asinh", "atan", "atan2", "atanh", "cbrt", "ceil", "clz32", "cos", "exp", "expm1", "floor", "fround", "hypot", "imul", "log1p", "log10", "log2", "max", "min", "pow", "random", "round", "sin", "sinh", "sqrt", "tan", "tanh", "trunc"];

var $resultVal = "acosh(1)+cos(PI/3)".toLowerCase();
try {
    //Iterate over each Math object/method
    $.each($mathKeywords, function (i, val) {
        //Convert val within array to a lower case form
        var $lowerKey = val.toLowerCase();
        var pattern = new RegExp("\b" + $lowerKey + "\b", "g");
        //See if pattern gives a match within $resultVal
        var $location = $resultVal.match(pattern);
        //Math keyword is found
        if ($location != null) {
            //replace the lowercase version of the math keyword with its properly cased version prepended 
            //with Math. i.e. cos becomes Math.cos and pi becomes Math.PI
            $resultVal = $resultVal.replace(pattern, "Math." + val);
        }
    });
    //Set the result element's value to an evaluation of $resultVal
    //A better implementation of the eval exists within the calc program
    console.log($resultVal);
    console.log(eval($resultVal));
} catch (err) {
    alert("Error: Cannot process expression due to " + err + ".");
}

输出：

acosh(1)+Math.cos(Math.PI/3)

（实际上是 Error: Cannot process expression due to ReferenceError: acosh is not defined. 但你明白了）

变化：

使用\b作为单词边界
在替换中使用模式（带单词边界）
使用 g 标志替换所有次出现。

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