{"id":16348,"date":"2022-10-15T07:41:36","date_gmt":"2022-10-15T02:11:36","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-how-to-get-the-number-of-pending-promises-closed\/"},"modified":"2022-10-15T07:41:36","modified_gmt":"2022-10-15T02:11:36","slug":"solved-how-to-get-the-number-of-pending-promises-closed","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-how-to-get-the-number-of-pending-promises-closed\/","title":{"rendered":"[Solved] How to get the number of pending promises? [closed]"},"content":{"rendered":"<p> [ad_1]<br \/>\n<\/p>\n<div id=\"answer-40207144\" class=\"answer js-answer accepted-answer js-accepted-answer\" data-answerid=\"40207144\" data-parentid=\"40206522\" data-score=\"1\" data-position-on-page=\"1\" data-highest-scored=\"1\" data-question-has-accepted-highest-score=\"1\" itemprop=\"acceptedAnswer\" itemscope itemtype=\"https:\/\/schema.org\/Answer\">\n<div class=\"post-layout\">\n<div class=\"votecell post-layout--left\"><\/div>\n<div class=\"answercell post-layout--right\">\n<div class=\"s-prose js-post-body\" itemprop=\"text\">\n<p>Here is a way to do it, where there is no need for an interval timer. It uses a queue of functions to call when the next HTTP response arrives (which makes the number of pending requests to come below 5):<\/p>\n<pre><code>var pending = 0;\nvar queue = [];\n\nfunction get(url){\n    return new Promise (function(resolve,reject){\n        function loop(retries = 3) {\n            var xhttp = new XMLHttpRequest();\n            xhttp.open(\"GET\",url,true);\n            xhttp.onload = function(){\n                pending--;\n                if (xhttp.status == 200){\n                    resolve(JSON.parse(xhttp.response));\n                }\n                else if (retries &gt; 0) {\n                    \/\/ retry by automatically relaunching the request:\n                    loop(retries-1);\n                } else {\n                    \/\/ give up\n                    reject(xhttp.statusText); \/\/ correct your spelling!\n                }\n                if (pending &lt; 5 &amp;&amp; queue.length) {\n                    \/\/ extract and execute the first of the queued actions:\n                    queue.shift()();\n                }\n            };\n            xhttp.onerror= function(){\n                reject(xhttp.statusText); \/\/ correct your spelling\n            };\n            xhttp.send()\n            pending++;\n        }\n        if (pending &gt;= 5) {\n            \/\/ Push the call we want to make for later execution in a queue:\n            queue.push(loop);\n        } else {\n            loop(); \/\/ try at the most 3 times\n        }\n    });\n}\n<\/code><\/pre>\n<p>Here is a snippet with a fake HTTPRequest object in order to simulate both the delay for when there are more than 5 pending requests, and a request that produces an error. All requests take 1 second to get a response, although the last one will produce an error status and will be retried 3 times, and as a consequence its promise only resolves after 3 seconds:<\/p>\n<\/p>\n<div class=\"snippet\" data-lang=\"js\" data-hide=\"false\" data-console=\"true\" data-babel=\"false\">\n<div class=\"snippet-code\">\n<pre class=\"snippet-code-js lang-js prettyprint-override\"><code>\/\/ Overwrite the real XMLHttpRequest with a dummy one, just for this snippet (skip this in your code!):\r\nfunction XMLHttpRequest() {\r\n    this.open = function(_, url) {\r\n        this.status = url.indexOf('fail') &gt; -1 ? 201 : 200;\r\n        this.response = JSON.stringify({text: 'Response from ' + url});\r\n        this.statusText = this.status == 200 ? 'OK' : 'Error status from ' + url;\r\n    };\r\n    this.send = function () {\r\n        setTimeout(this.onload.bind(this), 1000);\r\n    }.bind(this);\r\n}\r\n\r\nvar pending = 0;\r\nvar queue = [];\r\n\r\nfunction get(url){\r\n    return new Promise (function(resolve,reject){\r\n        function loop(retries = 3) {\r\n            var xhttp = new XMLHttpRequest();\r\n            xhttp.open(\"GET\",url,true);\r\n            xhttp.onload = function(){\r\n                pending--;\r\n                if (xhttp.status == 200){\r\n                    resolve(JSON.parse(xhttp.response));\r\n                }\r\n                else if (retries &gt; 0) {\r\n                    \/\/ retry by automatically relaunching the request:\r\n                    loop(retries-1);\r\n                } else {\r\n                    \/\/ give up\r\n                    reject(xhttp.statusText); \/\/ correct your spelling!\r\n                }\r\n                if (pending &lt; 5 &amp;&amp; queue.length) {\r\n                    \/\/ extract and execute the first of the queued actions:\r\n                    queue.shift()();\r\n                }\r\n            };\r\n            xhttp.onerror= function(){\r\n                reject(xhttp.statusText); \/\/ correct your spelling\r\n            };\r\n            xhttp.send()\r\n            pending++;\r\n        }\r\n        if (pending &gt;= 5) {\r\n            \/\/ Push the call we want to make for later execution in a queue:\r\n            queue.push(loop);\r\n        } else {\r\n            loop(); \/\/ try at the most 3 times\r\n        }\r\n    });\r\n}\r\n\r\n\/\/ Example series of calls to illustrate the effect of more than 5 simultanious requests\r\n\/\/ and the 3 retries for an error producing request:\r\nconsole.log('start');\r\nget('example.com?1').then( function(obj) { console.log(obj.text) });\r\nget('example.com?2').then( function(obj) { console.log(obj.text) });\r\nget('example.com?3').then( function(obj) { console.log(obj.text) });\r\nget('example.com?4').then( function(obj) { console.log(obj.text) });\r\nget('example.com?5').then( function(obj) { console.log(obj.text) });\r\nget('example.com?6').then( function(obj) { console.log(obj.text) });\r\nget('example.com?7').then( function(obj) { console.log(obj.text) });\r\nget('example.com?fail').catch( function(msg) { console.log(msg) });<\/code><\/pre>\n<pre class=\"snippet-code-css lang-css prettyprint-override\"><code>.as-console-wrapper { max-height: 100% !important; top: 0; }<\/code><\/pre>\n<\/div>\n<\/div><\/div>\n<div class=\"mt24\"><\/div>\n<\/div>\n<p>            <span class=\"d-none\" itemprop=\"commentCount\">1<\/span> <\/p><\/div>\n<\/div>\n<p>[ad_2]<\/p>\n<p>solved How to get the number of pending promises? [closed] <\/p>\n","protected":false},"excerpt":{"rendered":"<p>[ad_1] Here is a way to do it, where there is no need for an interval timer. It uses a queue of functions to call when the next HTTP response arrives (which makes the number of pending requests to come below 5): var pending = 0; var queue = []; function get(url){ return new Promise &#8230; <a title=\"[Solved] How to get the number of pending promises? [closed]\" class=\"read-more\" href=\"https:\/\/jassweb.com\/solved\/solved-how-to-get-the-number-of-pending-promises-closed\/\" aria-label=\"More on [Solved] How to get the number of pending promises? [closed]\">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":[898,333,2982],"class_list":["post-16348","post","type-post","status-publish","format-standard","hentry","category-solved","tag-ecmascript-6","tag-javascript","tag-promise"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>[Solved] How to get the number of pending promises? 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