document.referrer if 语句不起作用答案

【问题标题】：document.referrer if statement is not workingdocument.referrer if 语句不起作用
【发布时间】：2019-07-25 02:33:56
【问题描述】：

document.referrer 条件总是显示前一个语句为真，但它不应该是

if (document.referrer == "https://parks.com/parks/falls" || "https://parks.com/parks/events/falls" || "https://parks.com/parks/promotions/falls" || "https://parks.com/parks/go-green/falls" || "https://parks.com/parks/info/falls") { 
console.log("Don't Show Modal - coming from a Falls page", document.referrer);
} else {
console.log("Show Modal - coming from some other Page", document.referrer);
$( window ).on('load', function() {
   console.log("modal firing");
   $('#modal').modal({
   backdrop: 'static',
   keyboard: false,
   show: true
   });
});
}

当用户从 Falls 页面进入网页时，模式不应显示。如果用户从任何 Falls 页面以外的页面进入网页，则应该显示模式。

【问题讨论】：

标签： javascript if-statement conditional-statements

【解决方案1】：

你的条件不对。您应该在每个“子条件”中将变量与常量进行比较。

if (document.referrer == "https://parks.com/parks/falls"
|| document.referrer == "https://parks.com/parks/events/falls"
|| document.referrer == "https://parks.com/parks/promotions/falls" 
|| document.referrer == "https://parks.com/parks/go-green/falls"
|| document.referrer == "https://parks.com/parks/info/falls") {

也许更短：

const domains = ["https://parks.com/parks/cummins-falls", "https://parks.com/parks/events/falls", "https://parks.com/parks/promotions/falls", "https://parks.com/parks/go-green/falls", "https://parks.com/parks/info/falls"];
if (domains.includes(document.referrer)) {

IE 支持

if (domains.indexOf(document.referrer) !== -1) {

【讨论】：

没问题。如果这是对您帮助最大的答案，请将其选为已接受。

【解决方案2】：

这是您的 if 子句实际返回的内容：

// prints "https://parks.com/parks/events/falls"
console.log(document.referrer == "https://parks.com/parks/cummins-falls" || "https://parks.com/parks/events/falls" || "https://parks.com/parks/promotions/falls" || "https://parks.com/parks/go-green/falls" || "https://parks.com/parks/info/falls")

这是因为使用 OR 运算符 (||)，如果无法将左侧表达式强制转换为 true，那么它将返回右侧的表达式。

因此，在您的情况下，document.referrer == "https://parks.com/parks/cummins-falls" 的计算结果为 false，因此它返回 "https://parks.com/parks/events/falls" 的结果，在 Javascript 中，布尔运算的计算结果为 true，因此它在 OR 运算符和后面的 OR 运算符。

有关详细信息，请参阅truthy concept 上的文档。

你真正想要的：

var falls = ["https://parks.com/parks/cummins-falls",  "https://parks.com/parks/events/falls", "https://parks.com/parks/promotions/falls", "https://parks.com/parks/go-green/falls", "https://parks.com/parks/info/falls"];

console.log(falls.indexOf(document.referrer) > -1);

【讨论】：

【解决方案3】：

您的情况不正确。你应该使用这个：

if (document.referrer == "https://parks.com/parks/cummins-falls" || document.referrer == "https://parks.com/parks/events/falls" || document.referrer == "https://parks.com/parks/promotions/falls" || document.referrer == "https://parks.com/parks/go-green/falls" || document.referrer == "https://parks.com/parks/info/falls") { 
    console.log("Don't Show Modal - coming from a Falls page", document.referrer);
} else {
    console.log("Show Modal - coming from some other Page", document.referrer);
}

【讨论】：