How does jquery determine whether a node exists?

Jquery method to determine whether a node exists: first use the length attribute to get the number of elements in the node object; then determine whether the number of elements obtained is greater than 0. If it is greater than 0, the node exists, otherwise it does not exist; syntax format " if ($(selector).length>0) {//Exists}".

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jquery determines whether a node exists

jquery

if ($("#map").length > 0) {
        console.log("true");
    } else {
        console.log("false");
    }

Supplement:js

if (document.getElementById("map")) {
        console.log("存在");
        console.log(document.getElementById("map"));
    } else {
        console.log("不存在");
        console.log(document.getElementById("map"));
    }

if (!!document.getElementById("map")) {
        console.log("true");
    } else {
        console.log("false");
    }

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