請告訴我差異正則表達式結果

Question

爲什麼ghi的結果與abc或def不同？

ABC的結果爲abc：ABCDEF

DEF的結果是DEF：ABCDEF

GHI的結果爲GHI：A- {1} -C- {3} -E- {5}

請讓我知道原因！

function abc(){ 
    var lang = "{0}-{1}-{2}-{3}-{4}-{5}"; 
    var args = ["a","b","c","d","e","f"]; 
    var exp = /\{(\d+)\}/; 
    var matches = exp.exec(lang); 
    while (matches) { 
     var index = parseInt(matches[1], 10); 
     lang  = lang.replace(matches[0], args[index]); 
     matches = exp.exec(lang); 
    } 
    console.log('abc: ' + lang); 
} 
abc(); 
function def(){ 
    var lang = "{0}-{1}-{2}-{3}-{4}-{5}"; 
    var args = ["a","b","c","d","e","f"]; 
    var exp = /\{(\d+)\}/g; 
    var matches = exp.exec(lang); 
    while (matches) { 
     var exp = /\{(\d+)\}/g; 
     var index = parseInt(matches[1], 10); 
     lang  = lang.replace(matches[0], args[index]); 
     matches = exp.exec(lang); 
    } 
    console.log('def: ' + lang); 
} 
def(); 
function ghi(){ 
    var lang = "{0}-{1}-{2}-{3}-{4}-{5}"; 
    var args = ["a","b","c","d","e","f"]; 
    var exp = /\{(\d+)\}/g; 
    var matches = exp.exec(lang); 
    while (matches) { 
     var index = parseInt(matches[1], 10); 
     lang  = lang.replace(matches[0], args[index]); 
     matches = exp.exec(lang); 
    } 
    console.log('ghi: ' + lang); 
} 
ghi(); 

Answer 1

功能ghi()需要重置RegExp對象的lastIndex內循環：

function ghi(){ 
    var lang = "{0}-{1}-{2}-{3}-{4}-{5}"; 
    var args = ["a","b","c","d","e","f"]; 
    var exp = /\{(\d+)\}/g; 
    while (matches = exp.exec(lang)) { 
     var index = parseInt(matches[1], 10); 
     lang  = lang.replace(matches[0], args[index]); 
     exp.lastIndex = 0; 
    } 
    console.log('ghi: ' + lang); 
} 

由於exp.lastIndex = 0;呼叫現在輸出將是相同的。

JavaScript的RegExp對象是有狀態的。使用全局標誌時，如果您調用的方法與對象相同，它將從上次匹配結束時的下一個索引處開始。