Roadmap

• roadmap
• overview

1.3

• Tuple types

1.4

enum

2.8

• Conditional Types

3.2

todo: https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-2.html

3.7

Optional Chaining Operator(可选链操作符)

Optional Chaining Operator can help us reduce some code when we judge foo.bar.baz as follow:

// Before
if (foo && foo.bar && foo.bar.baz) {
  // ...
}

// After
if (foo?.bar?.baz) {
  // ...
}

?:: check in undefined and null.

undefined ?: 1 // undefined
null ?: 1      // undefined
0 ?: 1         // 1
'' ?: 1        // 1
NaN ?: 1       // 1

&& has different behaviour. Not only undefined and null, but falsy value will be also checked. eg:

undefined && 1 // undefined
null && 1      // null
0 && 1         // 0
'' && 1        // ''
NaN && 1       // NaN

Nullish Coalescing Operator(空值合并操作符)

?? means you can take the value that isn't undefined or null.

undefined ?? 1 // 1
null ?? 1      // 1
0 ?? 1         // 0
'' ?? 1        // ''

You can use it when using 0 as true such as:

if (typeof value !== 'number') return
// before
let valueStash = value === 0 || value ? value : defaultValue

// after
let valueStash = value ?? defaultValue

|| has different behaviour. Not only undefined and null, but falsy value will be also checked. eg:

undefined || 1 // 1
null || 1      // 1
0 || 1         // 1
'' || 1        // 1