I want to join two strings each representing a relative URL in Javascript.
I want to join the base URL http://www.adress.com/more/evenmore with the following examples:
../../adress (with the expected output: http://www.adress.com/adress)
../adress (with the expected output http://www.adress.com/more/adress)
What would be the best way? I was thinking of using regexp and checking
how many ../ preceed the relative URL, then subtracting that amount from the baseurl and adding them to what is left.
8 years later, many browsers (except for Internet Explorer) support the URL constructor (URL(url [, base])).
> new URL('../address', 'http://www.adress.com/more/evenmore/').href
"http://www.adress.com/more/address"
> new URL('../../address', 'http://www.adress.com/more/evenmore/').href
"http://www.adress.com/address"
The following function decomposes the URL then resolves it.
function concatAndResolveUrl(url, concat) {
var url1 = url.split('/');
var url2 = concat.split('/');
var url3 = [ ];
for (var i = 0, l = url1.length; i < l; i ++) {
if (url1[i] == '..') {
url3.pop();
} else if (url1[i] == '.') {
continue;
} else {
url3.push(url1[i]);
}
}
for (var i = 0, l = url2.length; i < l; i ++) {
if (url2[i] == '..') {
url3.pop();
} else if (url2[i] == '.') {
continue;
} else {
url3.push(url2[i]);
}
}
return url3.join('/');
}
Using URI.js (urijs - npm): absoluteTo():
function joinUrl(baseUrl, url) {
var theUrl = new URI(url);
if (theUrl.is("relative")) {
theUrl = theUrl.absoluteTo(baseUrl);
}
return theUrl.toString();
}
The ECMAScript URL Web API mentioned by #ning is a good place to start: especially as it is available in vanilla JS implementations (Node, etc.) and doesn't require you to use a library that does something the implementation nowq already accomplishes. Consulting the MDN documentation, more specifically the examples, is a great place to start.
Borrowing (somewhat) directly from their documentation:
let m = 'https://developer.mozilla.org';
// ... omitted
let d = new URL('/en-US/docs', m);
If you were to do the above, then console.log the .toString of the constructed URL object, your output would be: 'https://developer.mozilla.org/en-US/docs'.
Importantly, if you consult the Syntax section of the documentation, you will note that the second argument is optional and the second argument (as seen in the above example) represents the base URL (though only in the case of two arguments being supplied).
If both argument values are absolute URLs, Web API honors the first and discards the second.
If you are working with Node.js, I would encourage you to look at the native path module for doing work on relative paths, again over using a library. The main motivation here is that spinning up your own algorithm (probably just a call to path here and there) is potentially better than introducing a library that will pull in several other dependencies that may introduce vulnerabilities and unnecessary bloat to your application (or just be too heavy weight for what you need).
However, if you are working on the front end, you won't have path available to you and - as mentioned in #cburgmer's answer comments - Web API's URL doesn't support the relative path case mentioned. In this case, you may need to look for a library to accomplish this for you; however, again, given the other answers, I'd consider trying out a home-spun approach.
To their credit, URI.js currently only integrates one non-dev. dependency and doesn't have a huge footprint.
Related
According to the fundamentals of CS
the search functionality of an unsorted list has to occur in O(n) time where as direct access into an array will occur in O(1) time for HashMaps.
So is it more performant to map an array into a dictionary and then access the element directly or should I just use includes? This question is specifically for JavaScript because I believe this would come down to core implementation details of how includes() and {} is implemented.
let y = [1,2,3,4,5]
y.includes(3)
or...
let y = {
1: true,
2: true
3: true
4: true
5: true
}
5 in y
It's true that object lookup occurs in constant time - O(1) - so using object properties instead of an array is one option, but if you're just trying to check whether a value is included in a collection, it would be more appropriate to use a Set, which is a (generally unordered) collection of values, which can also be looked up in linear time. (Using a plain object instead would require you to have values in addition to your keys, which you don't care about - so, use a Set instead.)
const set = new Set(['foo', 'bar']);
console.log(set.has('foo'));
console.log(set.has('baz'));
This will be useful when you have to look up multiple values for the same Set. But, adding items to the Set (just like adding properties to an object) is O(N), so if you're just going to look up a single value, once, there's no benefit to this nor the object technique, and you may as well just use an array includes test.
Updated 04/29/2020
As the commenter rightly pointed out it would seem V8 was optimizing out the array includes calls. An updated version that assigns to a var and uses it produces more expected results. In that case Object address is fastest, followed by Set has and in a distant third is Array includes (on my system / browser).
All the same, I do stand by my original point, that if making micro-optimizations it is worth testing assumptions. Just make sure your tests are valid ;)
Original
Well. Despite the obvious expectation that Object address and Set has should outperform Array includes, benchmarks against Chrome indicate that implementation trumps expectation.
In the benches I ran against Chrome Array includes was far and away the best performer.
I also tested locally with Node and got more expected results. In that Object address wins, followed closely by Set has, then Array includes was marginally slower than both.
Bottom line is, if you're making micro-optimizations (not recommending that) it's worth benchmarking rather than assuming which might be best for your particular case. Ultimately it comes down to the implementation, as your question implies. So optimizing for the target platform is key.
Here's the results I got:
Node (12.6.0):
ops for Object address 7804199
ops for Array includes 5200197
ops for Set has 7178483
Chrome (75.0):
https://jsbench.me/myjyq4ixs1/1
This isn't necessarily a direct answer to the question but here is a related performance test I ran real quick in my chrome dev tools
function getRandomInt(max) {
return Math.floor(Math.random() * max);
}
var arr = [1,2,3];
var t = performance.now();
for (var i = 0; i < 100000; i++) {
var x = arr.includes(getRandomInt(3));
}
console.log(performance.now() - t);
var t = performance.now();
for (var i = 0; i < 100000; i++) {
var n = getRandomInt(3);
var x = n == 1 || n == 2 || n == 3;
}
console.log(performance.now() - t);
VM44:9 9.100000001490116
VM44:16 5.699999995529652
I find the array includes syntax nice to look at, so I wanted to know if the performance was likely to be an issue the way I use it, for checking if a variable is one of a set of enums for instance. It doesn't seem to be much of an impact for situations like this with a short list. Then I ran this.
function getRandomInt(max) {
return Math.floor(Math.random() * max);
}
var t = performance.now();
for (var i = 0; i < 100000; i++) {
var x = [1,2,3].includes(getRandomInt(3));
}
console.log(performance.now() - t);
var t = performance.now();
for (var i = 0; i < 100000; i++) {
var n = getRandomInt(3);
var x = n == 1 || n == 2 || n == 3;
}
console.log(performance.now() - t);
VM83:8 12.600000001490116
VM83:15 4.399999998509884
and so the way I actually use it and like lookin at it is quite worse with performance, despite still not being very significant unless run a few million times, so using it inside of an Array.filter that may run a lot as a react redux selector may not be a great idea like I was about to do when I decided to test this.
I have a piece of JS code which parses through a file, then associated the array with a key-value pair map, and then iterates it through it to find the proper city name with a .includes method. My problem is that the final field (where the function in question is called) works fine on my end for both Chrome and Firefox. It does not work for some reason for my group members.
This is the JS snippet that does the iterating:
Edit: this is how the file is being opened:
var rawFile = new XMLHttpRequest();
rawFile.open("GET", "../data/myFile.txt", false);
for (var i = 0; i < allText.length; i++) {
if (i % 2 == 0) {
myMap[allText[i]] = allText[i + 1];
}
}
var city = document.getElementById("city").value;
for (var key in myMap) {
if (myMap.hasOwnProperty(key)) {
if (myMap[key].toLowerCase().includes(city.toLowerCase())) {
document.getElementById("city").value = myMap[key]
document.getElementById("zipcode").value = key;
}
}
}
This is the html part that calls it:
<label for="myLabel">City: </label>
<input type="text" name="myLabel" id="myLabel" onblur="readTextFile()">
What exactly is the problem and how can I troubleshoot it as it makes no sense to me, coming from the world of Java and C++, where I have never faced such an issue before. If you are wondering why the JS might be kinda ugly, it is the result of a student with a teacher who thinks that showing W3Schools examples is equivalent to good teaching.
Javascript includes function may work erratically due to some browsers not supporting it. You need to be wise while choosing the javascript functions specially when mozilla may have some functions which are not supported on some browsers. W3schools also provides a list of Browser support for a function. Check the link below for that list for includes function:
http://www.w3schools.com/jsref/jsref_includes.asp
Alternatively, you can use indexOf function like:
myMap[key].toLowerCase().indexOf(city.toLowerCase()) >= 0
I have myself faced issues with includes function hence providing you a workaround. Happy programming.
My code need to execute a forumla (like Math.pow(1.05, mainObj.smallObj.count)).
My path is :
var path = mainObj.smallObj.count;
as you can see.
If needed, my code can split all variable names from this path and put it in an array to have something like :
var path = ["mainObj", "smallObj", "count"];
Since I don't want to use eval (this will cause memory leaks as it will be called many times every seconds), how can I access it from window?
Tried things like window["path"] or window.path.
If it is always unclear, let me know.
Thanks in advance for any help.
EDIT: forget to tell that some config are written in JSON, so when we take the formula, it's interpreted as "Math.pow(1.05, mainObj.smallObj.count)" so as a string.
I would say there are better solutions then eval, but it depends how the forumla can be structured. It could be precompiled using new Function (this is also some kind of eval) but allowing it to be called multiple times without the need to recompile for each invocation. If it is done right it should perform better then an eval.
You could do something like that:
var formula = {
code : 'Math.pow(1.05, mainObj.smallObj.count)',
params : ['mainObj']
}
var params = formula.params.slice(0);
params.push('return '+formula.code);
var compiledFormula = Function.apply(window, params);
//now the formula can be called multiple times
var result = compiledFormula({
smallObj: {
count: 2
}
});
You can get the path part reconciled by recursively using the bracket notation:
window.mainObj = { smallObj: { count: 2 } };
var path = ["mainObj", "smallObj", "count"];
var parse = function (obj, parts) {
var part = parts.splice(0, 1);
if (part.length === 0) return obj;
obj = obj[part[0]];
return parse(obj, parts);
};
var value = parse(window, path);
alert(value);
Basically, parse just pulls the first element off the array, uses the bracket notation to get that object, then runs it again with the newly shortened array. Once it's done, it just returns whatever the result of the last run is.
That answers the bulk of your question regarding paths. If you're trying to interpret the rest of the string, #t.niese's answer is as good as any other. The real problem is that you're trusting code from an external source to run in the context of your app, which can be a security risk.
I have been going through the Google chrome APIs in order to work on an extension and the processes regarding it. I stumbled upon the chrome.webRequest https://developer.chrome.com/extensions/webRequest#event-onBeforeRequest I have been tinkering with the syntax but I am lost with it because I'm relatively new to programming and using the chrome APIs
What I was thinking was using chrome.webRequest.onBeforeRequest.addListener(function callback) and then making it use chrome.tabs.remove to remove the tab is it matches the array but I am not sure how to do that
I have this for the removing of the tab using the google chrome match filters
var urlArray= ["*://facebook.com/*", "*://example.com/*", "*://google.com/*" ];
chrome.tabs.onCreated.addListener(function (tab) {
for (var i = 0, len = urlArray.length; i < len; i++) {
if (tab.url.indexOf(urlArray[i]) > -1) {
chrome.tabs.remove(tab.id);
alert("things");
break;
}
}
});
The problem in your code is that, if you check for "*somestring*", the .indexOf() function will actually look for that exact string, meaning that asterisks aren't used as a wildcard, and will only match if the string contains them.
Here's an example:
"hello".indexOf("*hello") // -1 there's no *
"123hello".indexOf("*hello") // -1 there's no *
"*hello".indexOf("*hello") // 0 here it is, in the first position
"123*hello".indexOf("*hello") // 3 and again, in the fourth position
So, in your case, you should use Regular Expressions, like this:
var urlExp= /https?\:\/\/(facebook|google|example)\.com/i;
chrome.tabs.onCreated.addListener(function (tab) {
if (urlExp.test(tab.url)) {
chrome.tabs.remove(tab.id);
alert("things");
}
});
I have a function e.g.
var test = function () {alert(1);}
How can I get the body of this function?
I assume that the only way is to parse the result of test.toString() method, but is there any other way? If parsing is the only way, what will be the regex to get to body? (help with the regex is extremly needed, because I am not familiar with them)
IF(!!!) you can get the toString(), then you can simply take the substring from the first indexOf("{") to the lastIndexOf("}"). So, something like this "works" (as seen on ideone.com):
var test = function () {alert(1);}
var entire = test.toString(); // this part may fail!
var body = entire.substring(entire.indexOf("{") + 1, entire.lastIndexOf("}"));
print(body); // "alert(1);"
2015 update
Upon revisiting the state of function decompilation, it can said that it's generally safe in certain well-considered use cases and enviroments (e.g: Node.js workers with user defined functions).
It should be put in the same bucket as eval, which is a powerful tool that has its place, but should only be used on rare occasions. Think twice, that's my only advice.
The conclusions from Kangax's new research:
It's still not standard
User-defined functions are generally looking sane
There are oddball engines (especially when it comes to source code
placement, whitespaces, comments, dead code)
There might be future oddball engines (particularly mobile or unusual
devices with conservative memory/power consumption)
Bound functions don't show their original source (but do preserve
identifier... sometimes)
You could run into non-standard extensions (like Mozilla's expression
closures)
ES6 is coming, and functions can now look very different than
they used to
Minifiers/preprocessors are not your friend
"function decompilation" — a process of getting
string representation of a Function object.
Function decompilation is generally
recommended against, as it is a
non-standard part of the language, and
as a result, leads to code being
non-interoperable and potentially
error-prone.
#kangax on comp.lang.javascript
Simplest Use-Case
If you just want to execute the body of the function (e.g. with eval or using the Worker API), you can simply add some code to circumvent all the pitfalls of extracting the body of the function (which, as mentioned by others, is a bad idea in general):
'(' + myFunction + ')()';
I am using this trick in this Worker-related JSFiddle.
Complete Function Serialization With Accurate Stacktrace
I also wrote a more complete library that can:
Serialize any kind of function to string
Be able to send that string representation anywhere else, execute it with any custom arguments, and be able to reproduce the original stacktrace
Check out my CodeBuilder code here.
Note that much of the code takes care of making sure that we get an accurate stacktrace, wherever we execute the serialized function at a later point in time.
This fiddle demonstrates a simplified version of that logic:
Use JSON.stringify to properly serialize the function (that comes in handy when, e.g., we want to make it part of a bigger serialization "data package").
We then wrap it in one eval to un-escape the "JSON-ish"-escaped string (JSON does not allow functions + code, so we must use eval), and then in another eval to get back the object we wanted.
We also use //# sourceMappingURL (or the old version //# sourceMappingURL) to show the right function name in the stacktrace.
You will find that the Stacktrace looks Ok, but it does not give you the correct row and column information relative to the file that we defined the serialized functions in, which is why my Codebuilder makes use of stacktracejs to fix that.
I use the CodeBuilder stuff in my (now slightly dated) RPC library where you can find some examples of how it is used:
serializeInlineFunction example
serializeFunction example
buildFunctionCall example
extending #polygenelubricants' answer:
using: .toString()
Testee:
var y = /* olo{lo} */
/* {alala} */function/* {ff} */ x/*{s}ls{
}ls*/(/*{*{*/)/* {ha-ha-ha} */
/*
it's a function
*/
{
return 'x';
// }
}
/*
*/
By indexOf and lastIndexOf:
function getFunctionBody(fn) {
function removeCommentsFromSource(str) {
return str.replace(/(?:\/\*(?:[\s\S]*?)\*\/)|(?:([\s;])+\/\/(?:.*)$)/gm, '$1');
}
var s = removeCommentsFromSource( fn.toString() );
return s.substring(s.indexOf('{')+1, s.lastIndexOf('}'));
};
getFunctionBody(y);
/*
"
return 'x'
"
*/
used: rm comments from js source
This code provides the body when using ES6 arrow functions like var testFn=(q)=>q+1;
function getFunctionBody(test){
var entire = test.toString(); // note: not safe-guarded; this part may fail like this!
return entire.substring((entire.indexOf("{")+1)||(entire.indexOf("=>")+2), entire.lastIndexOf("}")!==-1?entire.lastIndexOf("}"):entire.length);
}
//testing/showcase code
var tests = [
function () {alert(1);},
()=>{return 1;},
q=>q+1
];
for (var i=0;i<tests.length;i++){
console.log(tests[i],getFunctionBody(tests[i]));
}
I originally submitted this code as an edit to polygenelubricants accepted answer, but it was rejected as the changes were considered to be too drastic.
var fn1 = function() {};
var fn2 = function() { alert("lol!"); };
Function.prototype.empty = function() {
var x = this.toString().match(/\s*function\s*\w*\s*\(.*?\)\s*{\s*}\s*;?\s*/);
return x != null;
};
alert(fn1.empty()); // true
alert(fn2.empty()); // false
'
Solução proposta pelo Paulo Torres no grupo A.P.D.A. no facebook.
you can try this functiion:
function extractFunctionBody(fn) {
var reg = /function \((.*)\)[ ]?{(.*)}$/g;
var match = reg.exec(fn.toString().replace(/\n/g, ";"));
if (match){
return match[2];
} else {
return "";
}
}
Try this:
/\{(\s*?.*?)*?\}/g.exec(test.toString())[0]
test.toString() will hold your entire declaration.
/{(\s*?.?)?}/g will match everything between your braces