Question

我正在使用以下代码复制另一个textarea的输入：

/**
 * Copies the values entered into the old description
 * into the new description, until the user focuses 
 * on the new description
 */
var DescriptionLinker = (function() {
    var elOldDescription,
        elNewDescription,
        linkIsBroken;

    this.init = function() {
        console.log('Initializing DescriptionLinker');
        elOldDescription = document.getElementById("old-description");
        elNewDescription = document.getElementById("new-description");
        linkIsBroken = false;

        linkDescriptions();
        watchLinkBreak();
    }

    // Assigns values to 'this'
    var finalize = function() {
        this.elOldDescription = elOldDescription;
        this.elNewDescription = elNewDescription;
    }

    var linkDescriptions = function() {
        elOldDescription.addEventListener("keyup", linkListener(), false);
    }

    var unlinkDescriptions = function() {
        elOldDescription.removeEventListener("keyup", linkListener(), false);
    }

    var linkListener = function(){
        elNewDescription.value = elOldDescription.value;
    }

    var watchLinkBreak = function() {
        console.log("Watching for link break");
        elNewDescription.addEventListener("focus", function(){
            unlinkDescriptions();
        });
    }

    finalize();
    return this;
})();

DescriptionLinker.init();

代码有效，但在我专注于文本区域之前，值不会出现在<textarea id="new-description"></textarea>中。如果我使用相同的匿名函数替换对linkerfunction()的调用，那么当我在new-description中输入时，值会正确显示在old-description textarea中。有什么想法吗？

为了澄清，以下方法正常：

var linkDescriptions = function() {
    elOldDescription.addEventListener("keyup", function(){ 
         elNewDescription.value = elOldDescription.value;
    }, false);
}
var unlinkDescriptions = function() {
    elOldDescription.removeEventListener("keyup", function(){ 
         elNewDescription.value = elOldDescription.value;
    }, false);
}

所有这一切的PS原因是从遗留系统过渡：p

Answer 1

当然！传递已定义的函数代替匿名函数时，省略()，否则只要编译它就会调用此函数。所以，改变

lOldDescription.addEventListener("keyup", linkListener(), false);

要

lOldDescription.addEventListener("keyup", linkListener, false);
                                                      ^^ bye bye ()

Javascript事件侦听因匿名或命名函数的使用而异

1 个答案: