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chaining methods?


jekillen
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I have developed a utility function for extracting path info from a string containing a (Unix style) file path:

basename: the last element in the path

dirname: the path info minus the last element.

 

 

replacing '//' with '/ ' solves situations where there may be empty array items from

splitting the path string around '/': the last char in the string may be '/', which

would produce an empty array item. Also, if the first char is '/', it will produce

and empty array element

 

The last line in the function to get dirname is

return pathArray.join('/').replace('//', '/').substring(0, this.length - 1);

 

replacing '//' on the end will produce '/', so that is remove in substring call

(but as I write this it is evident that it needs a bit of work: do substring call

only if the last char is in fact '/')

 

it doesn't work: nothing is returned, not even an error.

 

if I do:

 

var path = pathArray.join('/').replace('//', '/');

return path.substring(0, path.length - 1)

 

I works

 

I would think that since (in the first case) there is no declared variable to

receive the results of join() and replace(), that 'this' would refer to the

results of join and replace.

 

So, the question is: why wouldn't it?

 

Thanks for time and attention

JK

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I have developed a utility function for extracting path info from a string containing a (Unix style) file path

 

 

Can you give an example of what it would do if it worked? The value of 'this' will vary depending on how a function is called.

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So, the question is: why wouldn't it?

this refers to the current scope, in that line it will refer to the scope context in which you call your function. It will default to the window object unless another scope is specified. Inside the substring function, if you saw the code for it, this would refer to the string object that substring got called on, but it doesn't refer to that object outside of the substring function when you call it.Saving the variable and using that to refer to the length will be the most efficient way. Academically, to do it all in one line you can split the string to an array of characters, reverse it, join it back to a string, use substring to get everything except the first character [i.e., substring(1)], and split, reverse, and join it again. Obviously that's a lot more work than just saving the variable and referring to the length that way.
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A short example:

 

for a path string like:

 

someDir/anotherDir/someFile

 

should produce

basename: someFIle

dirname: someDir/anotherDir (without trailing /, IE someDir/anotherDir/ )

 

the following is the utility itself, for the sake of sharing:

 

function _getPathInfo(a) { // a: string, dir/file path var getDirName = function(path) { var pathArray = [] pathArray = path.split('/'); pathArray[pathArray.length - 1] = ''; // remove last item var pathOut = pathArray.join('/').replace('//', '/'); return pathOut.substring(0, pathOut.length - 1) // doesn't work: // pathArray.join('/').replace('//', '/').substring(0, this.length - 1); } var getBaseName = function(path) { var pathArray = [] pathArray = path.split('/'); return pathArray[pathArray.length - 1] } this.dirname = getDirName(a); this.basename = getBaseName(a); }

 

In the head script:

// testCase is the id of a text input element to enter arbitrary path string

// getIt is the id of a button input element to run the code.

// alert produces 'basename: here dirname:' for test case input: '/going/to/here'

// It should produce 'basename: here dirname: /going/to'

 

window.onload = function() { var test = function(e) { var path = document.getElementById('testCase') if(path && path.value) { var pathInfo = new _getPathInfo(path.value) alert('basename: '+pathInfo.basename+' dirname: '+pathInfo.dirname) } } var tester = document.getElementById('getIt') if(tester) { tester.addEventListener('click', function(e){test(e)}, false) } }

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OK, my way is ugly.

function breaker(str1){var str = str1.trim();var len = str.length;var last0 = 0;var last1 = 0;var file = '';var path = '';if (len>0){  last0 = str.lastIndexOf('/');  last1 = str.lastIndexOf('');}if (last0>-1 && len-1>last0){ file = str.substr(last0+1); path = str.substr(0,last0);}else if (last1>-1 && len-1>last1){ file = str.substr(last1+1); path = str.substr(0,last1);}else if(last0==-1 && last1==-1){ file = str; path = '';}alert('str=['+ str +'] nfile=['+ file +'] npath=['+ path +']');}//end of function
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It looks like I provoked a good discussion

 

I have since significantly revised and expanded the utility

detects if the input has any instances of / and returns empty dirname value

filters out instances of ../ and ..

removes unnecressary /

returns anonymous object literals instead of setting public member variables.

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