如何在 JavaScript 中链式匹配和替换正则表达式

Question

str="abc { return false;}"

I just want to get the word "false" from the string "str", as follows,

str.match(/return \w+;/g).replace(/return/,"")

It 's wrong ! How can I correct this expression to get the desired word?

Answer 1

str.match will return an array with matching elements, not a single string. This is why .replace fails. A quick fix would be to add [0] to replace on the first array element like so: str.match(/return \\w+;/g)[0].replace(/return/,"")

However, this will return false; (not exactly what you want) and it will fail when there's no match at all: "Uncaught TypeError: Cannot read property '0' of null"

A better way would be to use capture groups with paranthesis:

var str= "abc { return false;}"
var re = /return (\w+);/g
var results = re.exec(str);

The result is again an array with the first element being the complete match, the second element is the first capture group: ["return false;", "false", index: 6, input: "abc { return false;}"]

Answer 2

If the goal is just to extract the "returned value" from the string(function text definition) - it can be achieved through one operation without chaining:

var str = "abc { return true;}";
console.log(str.match(/return (\w+?);/)[1]); // outputs "true"