我正在尝试创建一个简单的JavaScript程序，它会提示您在页面加载时输入一个句子。然后将该句子分成由空格“”分隔的数组。
我目前的问题是它根本没有将任何东西转换成大写或小写。我似乎无法理解为什么和一些帮助将不胜感激。
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>for-loop replacement exercise</title>
<script language="JavaScript" type="text/JavaScript">
var wordString = prompt("Please enter a sentence: ", 0);
var processedString;
var cont = boolean(true);
// this function is called upon page startup
function startMeUp() {
do {
wordString;
if (wordString == "") {
cont = boolean(false);
}
} while(cont);
processString(wordString);
document.write(processedString);
}
// this function is attempting to iterate through a array of strings and anything that is 4 characters long it is put to lower case
// otherwise if the iteration is less than 4 its put to upper case
function processString(someInput) {
var wordArray = someInput.split(" ");
var lengArray = wordArray.length;
for (var i = 0; i < lengArray; i++) {
if (lengArray[i] == 4) {
wordArray[i].toLowerCase();
} else if (lengArray[i] < 4) {
wordArray[i].toUpperCase();
}
}
processedString = wordArray.toString();
}
</script>
</head>
<body onload="startMeUp();">
</body>
</html>
尝试将返回值赋给数组索引，而不是只调用函数而不是存储它：
wordArray[i] = wordArray[i].toLowerCase();
首先你没有打电话给startMeUp()，所以我补充说。接下来，您可以使用map()简化代码。
var wordString = prompt("Please enter a sentence: ", '');
startMeUp();
function startMeUp() {
document.write(processString(wordString));
}
function processString(someInput) {
return someInput.split(" ").map(v => {
if (v.length == 4) return v.toLowerCase()
if (v.length < 4) return v.toUpperCase()
return v
}).join(' ')
}