diff --git a/1-js/02-first-steps/10-ifelse/article.md b/1-js/02-first-steps/10-ifelse/article.md index b3ab5997..1e12fa7b 100644 --- a/1-js/02-first-steps/10-ifelse/article.md +++ b/1-js/02-first-steps/10-ifelse/article.md @@ -1,12 +1,12 @@ # Conditional operators: if, '?' -Sometimes we need to perform different actions based on a condition. +Sometimes, we need to perform different actions based on different conditions. -There is the `if` statement for that and also the conditional (ternary) operator for conditional evaluation which we will be referring as the “question mark” operator `?` for simplicity. +To do that, we use the `if` statement and the conditional (ternary) operator which we will be referring to as the “question mark” operator `?` for simplicity. ## The "if" statement -The `if` statement gets a condition, evaluates it and, if the result is `true`, executes the code. +The `if` statement evaluates a condition and, if the condition's result is `true`, executes a block of code. For example: @@ -18,9 +18,9 @@ if (year == 2015) alert( 'You are right!' ); */!* ``` -In the example above, the condition is a simple equality check: `year == 2015`, but it can be much more complex. +In the example above, the condition is a simple equality check (`year == 2015`), but it can be much more complex. -If there is more than one statement to be executed, we have to wrap our code block inside curly braces: +If we want to execute more than one statement, we have to wrap our code block inside curly braces: ```js if (year == 2015) { @@ -29,15 +29,15 @@ if (year == 2015) { } ``` -It is recommended to wrap your code block with curly braces `{}` every time with `if`, even if there is only one statement. That improves readability. +We recommend wrapping your code block with curly braces `{}` every time you use an `if` statement, even if there is only one statement to execute. Doing so improves readability. ## Boolean conversion -The `if (…)` statement evaluates the expression in parentheses and converts it to the boolean type. +The `if (…)` statement evaluates the expression in its parentheses and converts the result to a boolean. Let's recall the conversion rules from the chapter : -- A number `0`, an empty string `""`, `null`, `undefined` and `NaN` become `false`. Because of that they are called "falsy" values. +- A number `0`, an empty string `""`, `null`, `undefined`, and `NaN` all become `false`. Because of that they are called "falsy" values. - Other values become `true`, so they are called "truthy". So, the code under this condition would never execute: @@ -48,7 +48,7 @@ if (0) { // 0 is falsy } ``` -...And inside this condition -- always works: +...and inside this condition -- it always will: ```js if (1) { // 1 is truthy @@ -56,7 +56,7 @@ if (1) { // 1 is truthy } ``` -We can also pass a pre-evaluated boolean value to `if`, like here: +We can also pass a pre-evaluated boolean value to `if`, like this: ```js let cond = (year == 2015); // equality evaluates to true or false @@ -68,11 +68,11 @@ if (cond) { ## The "else" clause -The `if` statement may contain an optional "else" block. It executes when the condition is wrong. +The `if` statement may contain an optional "else" block. It executes when the condition is false. For example: ```js run -let year = prompt('In which year was ECMAScript-2015 specification published?', ''); +let year = prompt('In which year was the ECMAScript-2015 specification published?', ''); if (year == 2015) { alert( 'You guessed it right!' ); @@ -83,12 +83,12 @@ if (year == 2015) { ## Several conditions: "else if" -Sometimes we'd like to test several variants of a condition. There is an `else if` clause for that. +Sometimes, we'd like to test several variants of a condition. The `else if` clause lets us do that. For example: ```js run -let year = prompt('In which year was ECMAScript-2015 specification published?', ''); +let year = prompt('In which year was the ECMAScript-2015 specification published?', ''); if (year < 2015) { alert( 'Too early...' ); @@ -99,13 +99,13 @@ if (year < 2015) { } ``` -In the code above JavaScript first checks `year < 2015`. If it is falsy it then goes to the next condition `year > 2015`, and otherwise shows the last `alert`. +In the code above, JavaScript first checks `year < 2015`. If that is falsy, it goes to the next condition `year > 2015`. If that is also falsy, it shows the last `alert`. -There can be more `else if` blocks. The ending `else` is optional. +There can be more `else if` blocks. The final `else` is optional. ## Ternary operator '?' -Sometimes we need to assign a variable depending on a condition. +Sometimes, we need to assign a variable depending on a condition. For instance: @@ -124,16 +124,16 @@ if (age > 18) { alert(accessAllowed); ``` -The so-called "ternary" or "question mark" operator lets us do that shorter and simpler. +The so-called "ternary" or "question mark" operator lets us do that in a shorter and simpler way. The operator is represented by a question mark `?`. The formal term "ternary" means that the operator has three operands. It is actually the one and only operator in JavaScript which has that many. The syntax is: ```js -let result = condition ? value1 : value2 +let result = condition ? value1 : value2; ``` -The `condition` is evaluated, if it's truthy then `value1` is returned, otherwise -- `value2`. +The `condition` is evaluated: if it's truthy then `value1` is returned, otherwise -- `value2`. For example: @@ -141,7 +141,9 @@ For example: let accessAllowed = (age > 18) ? true : false; ``` -Technically, we can omit parentheses around `age > 18`. The question mark operator has a low precedence. It executes after the comparison `>`, so that'll do the same: +Technically, we can omit the parentheses around `age > 18`. The question mark operator has a low precedence, so it executes after the comparison `>`. + +This example will do the same thing as the previous one: ```js // the comparison operator "age > 18" executes first anyway @@ -149,10 +151,10 @@ Technically, we can omit parentheses around `age > 18`. The question mark operat let accessAllowed = age > 18 ? true : false; ``` -But parentheses make the code more readable, so it's recommended to use them. +But parentheses make the code more readable, so we recommend using them. ````smart -In the example above it's possible to evade the question mark operator, because the comparison by itself returns `true/false`: +In the example above, you can avoid using the question mark operator because the comparison itself returns `true/false`: ```js // the same @@ -162,7 +164,7 @@ let accessAllowed = age > 18; ## Multiple '?' -A sequence of question mark `?` operators allows returning a value that depends on more than one condition. +A sequence of question mark operators `?` can return a value that depends on more than one condition. For instance: ```js run @@ -176,14 +178,14 @@ let message = (age < 3) ? 'Hi, baby!' : alert( message ); ``` -It may be difficult at first to grasp what's going on. But after a closer look we can see that it's just an ordinary sequence of tests. +It may be difficult at first to grasp what's going on. But after a closer look, we can see that it's just an ordinary sequence of tests: 1. The first question mark checks whether `age < 3`. -2. If true -- returns `'Hi, baby!'`, otherwise -- goes after the colon `":"` and checks for `age < 18`. -3. If that's true -- returns `'Hello!'`, otherwise -- goes after the next colon `":"` and checks for `age < 100`. -4. If that's true -- returns `'Greetings!'`, otherwise -- goes after the last colon `":"` and returns `'What an unusual age!'`. +2. If true -- it returns `'Hi, baby!'`. Otherwise, it continues to the expression after the colon '":"', checking `age < 18`. +3. If that's true -- it returns `'Hello!'`. Otherwise, it continues to the expression after the next colon '":"', checking `age < 100`. +4. If that's true -- it returns `'Greetings!'`. Otherwise, it continues to the expression after the last colon '":"', returning `'What an unusual age!'`. -The same logic using `if..else`: +Here's how this looks using `if..else`: ```js if (age < 3) { @@ -210,15 +212,15 @@ let company = prompt('Which company created JavaScript?', ''); */!* ``` -Depending on the condition `company == 'Netscape'`, either the first or the second part after `?` gets executed and shows the alert. +Depending on the condition `company == 'Netscape'`, either the first or the second expression after the `?` gets executed and shows an alert. -We don't assign a result to a variable here. The idea is to execute different code depending on the condition. +We don't assign a result to a variable here. Instead, we execute different code depending on the condition. -**It is not recommended to use the question mark operator in this way.** +**We don't recommend using the question mark operator in this way.** -The notation seems to be shorter than `if`, which appeals to some programmers. But it is less readable. +The notation is shorter than the equivalent `if` statement, which appeals to some programmers. But it is less readable. -Here is the same code with `if` for comparison: +Here is the same code using `if` for comparison: ```js run no-beautify let company = prompt('Which company created JavaScript?', ''); @@ -232,6 +234,6 @@ if (company == 'Netscape') { */!* ``` -Our eyes scan the code vertically. The constructs which span several lines are easier to understand than a long horizontal instruction set. +Our eyes scan the code vertically. Code blocks which span several lines are easier to understand than a long, horizontal instruction set. -The idea of a question mark `?` is to return one or another value depending on the condition. Please use it for exactly that. There is `if` to execute different branches of the code. +The purpose of the question mark operator `?` is to return one value or another depending on its condition. Please use it for exactly that. Use `if` when you need to execute different branches of code.