{"id":12074,"date":"2022-09-29T13:05:45","date_gmt":"2022-09-29T07:35:45","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-reading-local-file-in-javascript-duplicate\/"},"modified":"2022-09-29T13:05:45","modified_gmt":"2022-09-29T07:35:45","slug":"solved-reading-local-file-in-javascript-duplicate","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-reading-local-file-in-javascript-duplicate\/","title":{"rendered":"[Solved] Reading local file in javascript [duplicate]"},"content":{"rendered":"

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The answer is not really, no.<\/p>\n

BUT there are some workarounds, depending on what you can get away with (supported browsers, etc)<\/em><\/strong><\/p>\n

When you grab a local file (I’m assuming you’re using <input type=\"file\"><\/code>, rather than partially supported, unstandardized methods), you get a \"change\"<\/code> event to subscribe to, but that change reflects the change in selected files, not a change in the contents of a particular file.<\/p>\n

Moving beyond that, if you have a Blob<\/code> or a File<\/code> which inherits from Blob<\/code>, you basically have a buffer full of data.<\/p>\n

That buffer isn’t going to dynamically update itself, based on changes elsewhere in the OS, nor does it support callback options to do so.<\/p>\n

Alternatively, from a blob or a file, you have the option to use URL.createObjectURL( file )<\/code>, which returns a temporary url, which references a file, rather than the content of the file. <\/p>\n

That said, any change to that file might then be reflected from subsequent calls to that URI.
\nThis isn’t something I’ve built to test, yet. <\/p>\n

There would be no callback; however, you could set up an interval-based heartbeat, to make an XHR call to that URI, and then compare the .responseText<\/code> with the previous .responseText<\/code>.<\/p>\n

Again, no guarantees, but that’s as close as I think you’re going to get to an answer, right now (while still in the realm of plugin\/extension-free solutions), and might just be worth an hour of working out a prototype, and a couple more, testing support (whether the link is live, rather than an initial representation, etc).<\/p>\n

var input = document.querySelector(\"input[type=\"file\"]\"), \/\/ client must open file, themselves\n    fileHandle = \"\", \/\/ this will be the url for the local file\n    content    = \"\", \/\/ this will be the latest contents of the file\n    previousContent = \"\"; \/\/ this will be the previous contents\n\nvar ms = 1000,\n    secs = 2,\n\n    pollId; \/\/ will be the process ID for the polling (so you can stop checking for changes, later).\n\n\/\/ wait for a file to be selected\ninput.addEventListener(\"change\", function (evt) {\n\n    var file = evt.target.files[0]; \/\/ grab the file object\n    fileHandle = URL.createObjectURL(file); \/\/ create a url which points to the local file\n\n    \/\/ create an interval to check for changes\n    pollId = setInterval(\n        getLatest(fileHandle, getCurrent, updateCurrent),\n        secs * ms\n     );\n});\n\nfunction updateCurrent (latest) {\n    current = latest;\n    doStuff(current);\n    \/\/ the text has changed; it's been updated;\n    \/\/ now call home or do something else\n}\n\nfunction getCurrent () { return current; }\n\nfunction getLatest (url, getCurrent, onchange) {\n    return function () {\n        \/\/ this isn't actually calling the network\n        \/\/ it's calling the local file\n        var xhr = new XMLHttpRequest();\n        xhr.open(\"GET\", url);\n\n        xhr.onload = function () {\n            var latest = xhr.responseText;\n            if (getCurrent() !== latest) { onchange(latest); }\n        };\n\n        xhr.send();\n    };\n}\n<\/code><\/pre>\n
You now have change polling, in supporting browsers.<\/p>\n<\/p><\/div>\n
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            1<\/span> <\/p><\/div>\n<\/div>\n
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solved Reading local file in javascript [duplicate] <\/p>\n","protected":false},"excerpt":{"rendered":"
[ad_1] The answer is not really, no. BUT there are some workarounds, depending on what you can get away with (supported browsers, etc) When you grab a local file (I’m assuming you’re using <input type=”file”>, rather than partially supported, unstandardized methods), you get a “change” event to subscribe to, but that change reflects the change … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[575,333,1224],"class_list":["post-12074","post","type-post","status-publish","format-standard","hentry","category-solved","tag-file-io","tag-javascript","tag-local-storage"],"yoast_head":"\n[Solved] Reading local file in javascript [duplicate] - JassWeb<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jassweb.com\/solved\/solved-reading-local-file-in-javascript-duplicate\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] Reading local file in javascript [duplicate] - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] The answer is not really, no. BUT there are some workarounds, depending on what you can get away with (supported browsers, etc) When you grab a local file (I’m assuming you’re using <input type="file">, rather than partially supported, unstandardized methods), you get a "change" event to subscribe to, but that change reflects the change ... 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