Update--Loops: while and for

Author: imidom

1-js/02-first-steps/12-while-for/article.md

@@ -1,10 +1,10 @@
 # Loops: while and for
 
-We often have a need to perform similar actions many times in a row.
+We often need to repeat actions.
 
-For example, when we need to output goods from a list one after another. Or just run the same code for each number from 1 to 10.
+For example, outputting goods from a list one after another or just running the same code for each number from 1 to 10.
 
-*Loops* are a way to repeat the same part of code multiple times.
+*Loops* are a way to repeat the same code multiple times.
 
 ## The "while" loop
 
@@ -31,11 +31,11 @@ while (i < 3) { // shows 0, then 1, then 2
 
 A single execution of the loop body is called *an iteration*. The loop in the example above makes three iterations.
 
-If there were no `i++` in the example above, the loop would repeat (in theory) forever. In practice, the browser provides ways to stop such loops, and for server-side JavaScript we can kill the process.
+If there were no `i++` in the example above, the loop would repeat (in theory) forever. In practice, the browser provides ways to stop such loops and in server-side JavaScript, we can kill the process.
 
-Any expression or a variable can be a loop condition, not just a comparison. They are evaluated and converted to a boolean by `while`.
+Any expression or variable can be a loop condition, not just comparisons: the condition is evaluated and converted to a boolean by `while`.
 
-For instance, the shorter way to write `while (i != 0)` could be `while (i)`:
+For instance, a shorter way to write `while (i != 0)` is `while (i)`:
 
 ```js run
 let i = 3;
@@ -68,7 +68,7 @@ do {
 } while (condition);
 ```
 
-The loop will first execute the body, then check the condition and, while it's truthy, execute it again and again.
+The loop will first execute the body, then check the condition, and, while it's truthy, execute it again and again.
 
 For example:
 
@@ -80,11 +80,11 @@ do {
 } while (i < 3);
 ```
 
-This form of syntax is rarely used except when you want the body of the loop to execute **at least once** regardless of the condition being truthy. Usually, the other form is preferred: `while(…) {…}`.
+This form of syntax should only be used when you want the body of the loop to execute **at least once** regardless of the condition being truthy. Usually, the other form is preferred: `while(…) {…}`.
 
 ## The "for" loop
 
-The `for` loop is the most often used one.
+The `for` loop is the most commonly used loop.
 
 It looks like this:
 
@@ -102,14 +102,14 @@ for (let i = 0; i < 3; i++) { // shows 0, then 1, then 2
 }
 ```
 
-Let's examine the `for` statement part by part:
+Let's examine the `for` statement part-by-part:
 
 | part  |          |                                                                            |
 |-------|----------|----------------------------------------------------------------------------|
 | begin | `i = 0`    | Executes once upon entering the loop.                                      |
-| condition | `i < 3`| Checked before every loop iteration, if fails the loop stops.              |
-| step| `i++`      | Executes after the body on each iteration, but before the condition check. |
-| body | `alert(i)`| Runs again and again while the condition is truthy                         |
+| condition | `i < 3`| Checked before every loop iteration. If false, the loop stops.              |
+| step| `i++`      | Executes after the body on each iteration but before the condition check. |
+| body | `alert(i)`| Runs again and again while the condition is truthy.                         |
 
 
 The general loop algorithm works like this:
@@ -121,9 +121,9 @@ Run begin
 → ...
 ```
 
-If you are new to loops, then maybe it would help if you go back to the example and reproduce how it runs step-by-step on a piece of paper.
+If you are new to loops, it could help to go back to the example and reproduce how it runs step-by-step on a piece of paper.
 
-Here's what exactly happens in our case:
+Here's exactly what happens in our case:
 
 ```js
 // for (let i = 0; i < 3; i++) alert(i)
@@ -140,7 +140,7 @@ if (i < 3) { alert(i); i++ }
 ```
 
 ````smart header="Inline variable declaration"
-Here the "counter" variable `i` is declared right in the loop. That's called an "inline" variable declaration. Such variables are visible only inside the loop.
+Here, the "counter" variable `i` is declared right in the loop. This is called an "inline" variable declaration. Such variables are visible only inside the loop.
 
 ```js run
 for (*!*let*/!* i = 0; i < 3; i++) {
@@ -149,7 +149,7 @@ for (*!*let*/!* i = 0; i < 3; i++) {
 alert(i); // error, no such variable
 ```
 
-Instead of defining a variable, we can use an existing one:
+Instead of defining a variable, we could use an existing one:
 
 ```js run
 let i = 0;
@@ -166,7 +166,7 @@ alert(i); // 3, visible, because declared outside of the loop
 
 ### Skipping parts
 
-Any part of `for` can be skipped.
+Any part of the `for` syntax can be skipped.
 
 For example, we can omit `begin` if we don't need to do anything at the loop start.
 
@@ -200,15 +200,15 @@ for (;;) {
 }
 ```
 
-Please note that the two `for` semicolons `;` must be present, otherwise it would be a syntax error.
+Please note that the two `for` semicolons `;` must be present. Otherwise, there would be a syntax error.
 
 ## Breaking the loop
 
-Normally the loop exits when the condition becomes falsy.
+Normally, a loop exits when its condition becomes falsy.
 
-But we can force the exit at any moment. There's a special `break` directive for that.
+But we can force the exit at any time using the special `break` directive.
 
-For example, the loop below asks the user for a series of numbers, but "breaks" when no number is entered:
+For example, the loop below asks the user for a series of numbers, "breaking" when no number is entered:
 
 ```js
 let sum = 0;
@@ -227,15 +227,15 @@ while (true) {
 alert( 'Sum: ' + sum );
 ```
 
-The `break` directive is activated at the line `(*)` if the user enters an empty line or cancels the input. It stops the loop immediately, passing the control to the first line after the loop. Namely, `alert`.
+The `break` directive is activated at the line `(*)` if the user enters an empty line or cancels the input. It stops the loop immediately, passing control to the first line after the loop. Namely, `alert`.
 
-The combination "infinite loop + `break` as needed" is great for situations when the condition must be checked not in the beginning/end of the loop, but in the middle, or even in several places of the body.
+The combination "infinite loop + `break` as needed" is great for situations when a loop's condition must be checked not in the beginning or end of the loop, but in the middle or even in several places of the body.
 
 ## Continue to the next iteration [#continue]
 
-The `continue` directive is a "lighter version" of `break`. It doesn't stop the whole loop. Instead it stops the current iteration and forces the loop to start a new one (if the condition allows).
+The `continue` directive is a "lighter version" of `break`. It doesn't stop the whole loop. Instead, it stops the current iteration and forces the loop to start a new one (if the condition allows).
 
-We can use it if we're done on the current iteration and would like to move on to the next.
+We can use it if we're done with the current iteration and would like to move on to the next one.
 
 The loop below uses `continue` to output only odd values:
 
@@ -249,9 +249,9 @@ for (let i = 0; i < 10; i++) {
 }
 ```
 
-For even values of `i` the `continue` directive stops body execution, passing the control to the next iteration of `for` (with the next number). So the `alert` is only called for odd values.
+For even values of `i`, the `continue` directive stops executing the body and passes control to the next iteration of `for` (with the next number). So the `alert` is only called for odd values.
 
-````smart header="The directive `continue` helps to decrease nesting level"
+````smart header="The `continue` directive helps decrease nesting"
 A loop that shows odd values could look like this:
 
 ```js
@@ -264,13 +264,13 @@ for (let i = 0; i < 10; i++) {
 }
 ```
 
-From a technical point of view it's identical to the example above. Surely, we can just wrap the code in the `if` block instead of `continue`.
+From a technical point of view, this is identical to the example above. Surely, we can just wrap the code in an `if` block instead of using `continue`.
 
-But as a side-effect we got one more nesting level (the `alert` call inside the curly braces). If the code inside `if` is longer than a few lines, that may decrease the overall readability.
+But as a side-effect, this created one more level of nesting (the `alert` call inside the curly braces). If the code inside of`if` is longer than a few lines, that may decrease the overall readability.
 ````
 
 ````warn header="No `break/continue` to the right side of '?'"
-Please note that syntax constructs that are not expressions cannot be used with the ternary operator `?`. In particular, directives such as `break/continue` are disallowed there.
+Please note that syntax constructs that are not expressions cannot be used with the ternary operator `?`. In particular, directives such as `break/continue` aren't allowed there.
 
 For example, if we take this code:
 
@@ -282,24 +282,24 @@ if (i > 5) {
 }
 ```
 
-...And rewrite it using a question mark:
+...and rewrite it using a question mark:
 
 
 ```js no-beautify
-(i > 5) ? alert(i) : *!*continue*/!*; // continue not allowed here
+(i > 5) ? alert(i) : *!*continue*/!*; // continue isn't allowed here
 ```
 
-...Then it stops working. The code like this will give a syntax error:
+...it stops working. Code like this will give a syntax error:
 
 
-That's just another reason not to use a question mark operator `?` instead of `if`.
+This is just another reason not to use the question mark operator `?` instead of `if`.
 ````
 
 ## Labels for break/continue
 
 Sometimes we need to break out from multiple nested loops at once.
 
-For example, in the code below we loop over `i` and `j` prompting for coordinates `(i, j)` from `(0,0)` to `(3,3)`:
+For example, in the code below we loop over `i` and `j`, prompting for the coordinates `(i, j)` from `(0,0)` to `(3,3)`:
 
 ```js run no-beautify
 for (let i = 0; i < 3; i++) {
@@ -318,7 +318,7 @@ alert('Done!');
 
 We need a way to stop the process if the user cancels the input.
 
-The ordinary `break` after `input` would only break the inner loop. That's not sufficient. Labels come to the rescue.
+The ordinary `break` after `input` would only break the inner loop. That's not sufficient--labels, come to the rescue!
 
 A *label* is an identifier with a colon before a loop:
 ```js
@@ -327,9 +327,7 @@ labelName: for (...) {
 }
 ```
 
-The `break <labelName>` statement in the loop breaks out to the label.
-
-Like here:
+The `break <labelName>` statement in the loop below breaks out to the label:
 
 ```js run no-beautify
 *!*outer:*/!* for (let i = 0; i < 3; i++) {
@@ -347,7 +345,7 @@ Like here:
 alert('Done!');
 ```
 
-In the code above `break outer` looks upwards for the label named `outer` and breaks out of that loop.
+In the code above, `break outer` looks upwards for the label named `outer` and breaks out of that loop.
 
 So the control goes straight from `(*)` to `alert('Done!')`.
 
@@ -358,10 +356,10 @@ outer:
 for (let i = 0; i < 3; i++) { ... }
 ```
 
-The `continue` directive can also be used with a label. In this case the execution jumps to the next iteration of the labeled loop.
+The `continue` directive can also be used with a label. In this case, code execution jumps to the next iteration of the labeled loop.
 
 ````warn header="Labels are not a \"goto\""
-Labels do not allow us to jump into an arbitrary place of code.
+Labels do not allow us to jump into an arbitrary place in the code.
 
 For example, it is impossible to do this:
 ```js
@@ -370,7 +368,7 @@ break label;  // jumps to label? No.
 label: for (...)
 ```
 
-The call to a `break/continue` is only possible from inside the loop, and the label must be somewhere upwards from the directive.
+A call to `break/continue` is only possible from inside a loop and the label must be somewhere above the directive.
 ````
 
 ## Summary
@@ -383,6 +381,6 @@ We covered 3 types of loops:
 
 To make an "infinite" loop, usually the `while(true)` construct is used. Such a loop, just like any other, can be stopped with the `break` directive.
 
-If we don't want to do anything on the current iteration and would like to forward to the next one, the `continue` directive does it.
+If we don't want to do anything in the current iteration and would like to forward to the next one, we can use the `continue` directive.
 
-`break/continue` support labels before the loop. A label is the only way for `break/continue` to escape the nesting and go to the outer loop.
+`break/continue` support labels before the loop. A label is the only way for `break/continue` to escape a nested loop to go to an outer one.