window.NRUM = window.NRUM || {};

今天看到这段代码，想问下第一句window.NRUM = window.NRUM || {}; 这个代表了什么意思。百度了下没搜到

<script> 
window.NRUM = window.NRUM || {};  
window.NRUM.config = {key:'27e86c0843344caca7ba9ea652d7948d',clientStart: +new Date()};    
function() {var n = document.getElementsByTagName('script')[0],s = document.createElement('script');s.type = 'text/javascript';s.async = true;s.src = '//nos.netease.com/apmsdk/napm-web-min-1.1.1.js';n.parentNode.insertBefore(s, n);})();     
</script>

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等同于

if(!window.NRUM){
    window.NRUM = {}
}

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看我以前回答 https://.com/q/1010000005880084/a-1020000005880121

是对window.NRUM的初始化