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From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups: comp.lang.javascript
Subject: Re: Instead of <iframe onload=...
Date: Mon, 22 May 2017 03:27:32 +0200
Organization: PointedEars Software (PES)
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Dr J R Stockton wrote:

> function Ink(Sauce, DefaultHeight) { var Fram
>   […]
>   Fram.onload = Inky(Fram, DefaultHeight)
                  ^^^^^
>   […]
> function Inky(Ifr, ExHi) {
>   // Autosize works in Firefox and MS IE (Edge?), else use ExHi
>   setTimeout(function() { Procrustes(Ifr, ExHi) } , 500) }

    [Unusual, highly questionable code style aside:]

JFTR, this is a common mistake.  This way the function Inky() would be 
called *before* the assignment to the “onload” property, and the “onload” 
property would be assigned the “undefined” value when either the “null” 
value or a reference to a Function instance is expected.  Such an assignment 
would result in a runtime error in earlier versions of Internet Explorer; 
later versions might have a setter for that property to ignore it and to 
keep the default “null” property value.

It is therefore unsurprising to me that the timeout delay would have to be 
set that high (500 ms) as calling Inky() does _not_ correspond with loading 
the iframe document.

Perhaps the following was sought for instead:

  iframe.onload = function () {
    inky(this, defaultHeight);
  };

However, usually one would wrap the iframe object into a custom object with 
appropriate initialization and methods instead of global functions (OOP: 
encapsulation, information hiding).  For example (quick hack):

  /* @namespace */
  var JRS = (function () {
    "use strict";

    /* @constructor */
    function _IframeWidget (target, source)
    {
      if (!(this instanceof _IframeWidget))
      {
        return new _IframeWidget(target, source);
      }

      this.target = target || document.createElement("iframe");

      Object.assign(this.target.style, {
        border: "2px solid red",
        width: "100%",
        margin: "0.5ex 0",
        background: "#FFE"
      });

      this.target.onload = function () {
        this.procrustes();
      }.bind(this);

      if (!target) document.body.appendChild(this.target);

      this.target.src = source;
    }

    Object.assign(_IFrameWidget.prototype, {
      /* @memberOf JRS.IFrameWidget.prototype */
      defaultHeight: …,

      procrustes: function (exHi) {
        // … this.target.contentDocument …
      }
    });

    Object.defineProperty(_IFrameWidget.prototype, "constructor", {
      /* @memberOf JRS.IFrameWidget.prototype */
      value: _IFrameWidget
    });

    return {
      /* @memberOf JRS */
      IframeWidget: _IFrameWidget
    };
  }());
 
-- 
PointedEars
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