使用正则表达式匹配左侧的东西

Question

Train from London to Boston - match 
Train from Boston to London 
Train from Cardif to London 
Bus from London to Paris - match 

如果伦敦出现在任何其他城市与正则表达式之前，我该如何匹配？我可以用JavaScript中的循环进行字符串匹配，但我认为正则表达式更好。

Answer 1

获取线路，其包括London to

var str = `Train from London to Boston - match 
 
Train from Boston to London 
 
Train from Cardif to London 
 
Bus from London to Paris - match`, 
 
    city = 'london'; 
 

 
console.log(
 
    str.match(new RegExp('^.*\\b' + city + '\\sto\\b.*$', 'gmi')) 
 
)

Regex explanation here

Answer 2

试试这个

\bLondon(?=\s*to\b) 

Regex demo

说明：
\：转义特殊字符sample
(?=…)：正向前查找sample
\s： “空白字符”：空格，制表，换行符，carr iage返回，垂直制表sample
*：零或更多次sample

的Javascript

var re = /\bLondon(?=\s*to\b)/g; 
var str = 'Train from London to Boston - match\nTrain from Boston to London\nTrain from Cardif to London\nBus from London to Paris - match'; 
var m; 

while ((m = re.exec(str)) !== null) { 
    if (m.index === re.lastIndex) { 
     re.lastIndex++; 
    } 
    // View your result using the m-variable. 
    // eg m[0] etc. 
}