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Double negation (!!) in javascript - what is the purpose? [duplicate]
...true
+0 to true
-0 to true
'' to true
NaN to true
false to true
All other expressions to false
Then the other ! negates it again. A concise cast to boolean, exactly equivalent to ToBoolean simply because ! is defined as its negation. It’s unnecessary here, though, because it’s only used as the...
scrapy xpath抓取节点的文本innerText、innerHTML、outerHTML - 更多技术 -...
scrapy xpath抓取节点的文本innerText、innerHTML、outerHTML假设抓取：<p> xx<b>x< b>< p> 抓取p节点本身，得到的内容：<p>xx<b>x< b>< p>response xpath(& 39; div[@class="question"] div[2] div[2] div[1] p[1]& 39;) extract() 抓 假设抓取：
<p>
xx<b>x</b>
</p>
scra...
xxx.sh: line x: [0: command not found - 脚本技术 - 清泛IT社区，为创新赋能！
由于if [ 后面没有加空格导致的。
if [ xxx ] 表达式前后都要有空格。
Discuz X 首页白板解决之道 - 建站技术 - 清泛IT论坛，有思想、有深度
...法，代码一段段的排查，在合适位置打印特定内容然后exit(0);查看结果，分析出现问题的大致位置。可以毫不夸张地说，排除法能够解决99.99%的疑难杂症。
3、白板的最核心原因是调用函数 ob_end_clean() 函数导致的，先将输出内容...
[es6] import, export, default cheatsheet - 更多技术 - 清泛网 - 专注C/C++及内核技术
[es6] import, export, default cheatsheetimport-export-default-require-commandjs-javascript-nodejs-es6有四种类型的导出：1、命名导出（每个模块可以有多个）2、默认导出（每个模块一个）3、混合命名和默认导出4、循环依赖1 Nameexports ------ lib js ------...
屏幕像素怎么设置成1080X1920? - App应用开发 - 清泛IT社区，为创新赋能！
如题，手机尺寸只能按给定的使用吗？1、网页端的分辨率只是预览用的，实际分辨率以测试设备为准：
2、手机/平板分辨率往往是固定的。但是模拟器一般来说是可以设置分辨率，详见：https://www.fun123.cn/reference/ ... 5%E4%BD%BF%...
Can't escape the backslash with regex?
I'm using the following regex
5 Answers
5
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C# List of objects, how do I get the sum of a property
... answered Dec 4 '10 at 4:11
Alex LEAlex LE
17.1k44 gold badges2626 silver badges2828 bronze badges
...
Changes in import statement python3
... relative to the current script/package.
Consider the following tree for example:
mypkg
├── base.py
└── derived.py
Now, your derived.py requires something from base.py. In Python 2, you could do it like this (in derived.py):
from base import BaseThing
Python 3 no longer supports t...
Passing arguments forward to another javascript function
...n copy it into an array then manipulate that before passing it along, for example: var copy = [].slice.call(arguments); <remove what you want> myFunc.apply(this, copy);
– Nick Craver♦
Feb 17 '12 at 11:18
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