javascript - 如何检测文本区域中的前一行是否为空

Question

是否可以检测文本区域中单行的结构。例如，这是我的文本区域及其内容

this is the first line in textarea
1234 this is the second line starting with 1234

this is the fourth line and the third line is empty

所以我想检测像 line 3 这样的空行，并检测像 line 2 这样的行的前 4 个字符。这可以通过 jQuery 或 JavaScript 实现吗？

Answer 1

textarea 中的值只是一个字符串，您可以在换行符处拆分它以获取每一行。

var arrayOfLines = $('textarea').val().split('\n');
var finalString = "";
var prevBoolean = false;
for (var i = 0; i < arrayOfLines.length; i++) {
    var line = arrayOfLines[i];

    if (line.length === 0) {
       console.log("empty line");
    } else {
        // if the first 4 characters of the line are "1234" set prevBoolean to true
        if (line.substring(0, 4) == "1234"){
            finalString += line + "\n";
            prevBoolean = true;
        } else {
            // add custom line, if the previous non-empty line started with "1234" and set prevBoolean back to false
            if (prevBoolean == true) {
                 prevBoolean = false;
                 finalString += "custom line" + "\n";
             } else {
                 finalString += line + "\n";
             }

        }
    }
}

// set the value of the textarea to the finalString
$('textarea').val(finalString);