Javascript替换方法说明

Question

1- $ 3 $ 2 $ 1的含义是:

var s = "The quick brown fox jumped over the lazy dog.";
var re = /(\S+)(\s+)(\S+)/g;
// Exchange each pair of words.
var result = s.replace(re, "$3$2$1");
document.write(result);

// Output:  quick The fox brown over jumps lazy the dog.

2-和$ 0,$ 1,$ 2 in:

function f2c(s1) {
    // Initialize pattern.
    var test = /(\d+(\.\d*)?)F\b/g;

    // Use a function for the replacement.
    var s2 = s1.replace(test,
      function($0,$1,$2)
           { 
           return((($1-32) * 5/9) + "C");
           }
        )
    return s2;
}
document.write(f2c("Water freezes at 32F and boils at 212F."));

// Output: Water freezes at 0C and boils at 100C.

请注意,感谢您的回复,我理解第1号,但是第2号有点难,我正在努力解决它.

谢谢,

优素福

Answer 1

1-在reg exp中,括号表示捕获模式,$ X表示对捕获元素的引用:

var re = /(\S+)(\s+)(\S+)/g;
            ^     ^    ^
            |     |    |
            $1    $2   $3

在这种模式中,替换它将$1$2$3采取3个匹配并反转它们,所以它将采取"快速"并将其变为"快速".

2- $ 0引用整个匹配的子表达式.给定的函数不会使用$ 0或$ 2,只需$ 1即可将°F转换为C°