5.5 Idioms

>>>

var obj = { text: 'ok'};

>>>

obj.missing || 'default'

"default"

As previously mentioned, boolean logic is commonly used to provide default values. The ?? nullish coalescing operator (introduced with ES11 in 2020) is a recent alternative in many cases.

>>>

obj && obj.text

"ok"

It is also common to use boolean logic to avoid issues with possible null references. The ?. optional chaining operator (introduced with ES11 in 2020) simplifies this further.

>>>

obj && print(obj);

A third way of using boolean conditions is the cond && operation idiom. This code style avoids an if statement for short operations.

>>>

[0, 1, true, false, '', ' ', null, undefined].filter(Boolean)

[1, true, " "]

The built-in Boolean function coerces any value into a boolean. This is useful when filtering out null or empty values from an array. But note that 0 and false are also removed.

>>>

new Array(4).fill(0).map(Math.random).map(v => v * 10).map(Math.floor).join('-')

"0-1-2-3"

Some objects, such as Array, have methods that either return a new instance or a reference to itself. This makes it possible to use method chaining to avoid intermediate result variables.

>>>

The console allows you to interact with the course material and examples. Use the following keys:

<Enter> — Execute the code
<Shift + Enter> — Add line break
<Arrow-Up> — Previous command in history
<Arrow-Down> — Next command in history

A special logging function is also available:

print(value) — Prints a value to the console.
print(value, true) — Prints a debug version of a value.

Console Learner — An interactive JavaScript course.