ECMAScript proposal: "use slow" directive.

proposal-use-slow-directive.md

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+# ECMAScript proposal: The "use slow" Directive
+- [Motivation](#motivation)
+- [Declaring](#declaring)
+- [Usage](#usage)
+
+## Motivation
+
+`"use slow";` defines that code should be executed slowly.\
+Basic performance decrease: x 2.
+
+## Declaring
+
+`"use slow";` Must be declared in a Directive Prologue
+
+At the beginning of a script:
+```js
+"use slow";
+console.log('slow code');
+```
+
+At the beginning of a function:
+```js
+console.log('normal');
+
+function slowFunction(){
+  "use slow";
+  console.log('slow');
+}
+```
+`"use slow";` affects only the function in which it is declared.
+
+## Usage
+Use slow can be be more than once. Slowdown effect is multiplied. Example:
+```js
+"use slow"; // x 2
+"use slow"; // x 2
+"use slow"; // x 2
+console.log('this code 8 times slower');
+```
+Use slow inside the function takes effect from the outside code or function:
+```js
+"use slow"; // x 2
+console.log('this code 2 times slower');
+
+function f(){
+  "use slow"; // x 2
+  console.log('this code 4 times slower');
+
+  return function g(){
+    "use slow"; // x 2
+    console.log('this code 8 times slower');
+  }
+}
+```