Javascript for循环直到 - 多个条件
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Javascript for loop until - multiple conditions
提问by Darren Sweeney
I am using javascript, using regex to scrape images from html code.
我正在使用 javascript，使用正则表达式从 html 代码中抓取图像。
I want the loop to run either until the script finds no more images or until it reaches 12.
我希望循环运行直到脚本找不到更多图像或直到它达到 12。
I'm trying the following but not working:
我正在尝试以下但不起作用：
var imgs = d.getElementsByTagName('img'), found = [];
for(var i=0,img; ((img = imgs[i]) || ( $i < 13)); i++)
Is this possible? Am I on the right lines?
这可能吗？我在正确的路线上吗？
Quite new to javascript but trying!
对 javascript 很陌生，但正在尝试！
回答by I Hate Lazy
You should use &&instead of ||. Also, $ishould be i.
你应该使用&&而不是||. 另外，$i应该是i。
for(var i=0, img; (img = imgs[i]) && (i < 12); i++)
found.push(img);
回答by Alnitak
Assuming that you want foundto contain those first 12:
假设您要found包含前 12 个：
var imgs = d.getElementsByTagName('img');
var found = [].slice.call(imgs, 0, 12);
You have to use [].slice.call(imgs, ...)instead of imgs.slice()because imgsis only a pseudo-array, and not a real array.
你必须使用[].slice.call(imgs, ...)而不是imgs.slice()因为imgs它只是一个伪数组，而不是一个真正的数组。
An alternative to writing [].sliceis Array.prototype.slice.
写作的另一种选择[].slice是Array.prototype.slice。
If you want to do something else inside the loop, just use the array created above to ensure that you only work on the first 12 images:
如果你想在循环中做其他事情，只需使用上面创建的数组来确保你只处理前 12 张图像：
for (var i = 0, n = found.length; i < n; ++i) {
// do something with found[i];
}
回答by epascarello
I personally hate when people do assignment in the condition clause of a forloop, since it looks like someone mistook an assignment (=) for a comparison (===or ==). Better to do the logic elsewhere.
我个人讨厌人们在for循环的条件子句中进行赋值，因为看起来有人将赋值 ( =)误认为是比较 ( ===or ==)。最好在别处做逻辑。
var imgs = d.getElementsByTagName('img'),
found = [],
i,
imgsLength = imgs.length,
max = imgsLength > 13 ? 13 : imgsLength;
for (i = 0; i < max; i++) {
found.push(imgs[i]);
}
or
或者
var imgs = d.getElementsByTagName('img'),
found = [],
i,
imgsLength = imgs.length;
for (i = 0; i < 13 && i < imgsLength; i++) {
found.push(imgs[i]);
}
