Angular expressions are based on JavaScript, but differ in some key ways. This guide walks through the similarities and differences between Angular expressions and standard JavaScript.
Value literals
Angular supports a subset of literal values from JavaScript.
Supported value literals
| Literal type | Example values |
|---|---|
| String | 'Hello', "World" |
| Boolean | true, false |
| Number | 123, 3.14 |
| Object | {name: 'Alice'} |
| Array | ['Onion', 'Cheese', 'Garlic'] |
| null | null |
Unsupported literals
| Literal type | Example value |
|---|---|
| Template string | \Hello ${name}`` |
| RegExp | /\d+/ |
Globals
Angular expressions support the following globals:
No other JavaScript globals are supported. Common JavaScript globals include Number, Boolean, NaN, Infinity, parseInt, and more.
Local variables
Angular automatically makes special local variables available for use in expressions in specific contexts. These special variables always start with the dollar sign character ($).
For example, @for blocks make several local variables corresponding to information about the loop, such as $index.
What operators are supported?
Supported operators
Angular supports the following operators from standard JavaScript.
| Operator | Example(s) |
|---|---|
| Add / Concatenate | 1 + 2 |
| Subtract | 52 - 3 |
| Multiply | 41 * 6 |
| Divide | 20 / 4 |
| Remainder (Modulo) | 17 % 5 |
| Parenthesis | 9 * (8 + 4) |
| Conditional (Ternary) | a > b ? true : false |
| And (Logical) | && |
| Or (Logical) | || |
| Not (Logical) | ! |
| Nullish Coalescing | const foo = null ?? 'default' |
| Comparison Operators | <, <=, >, >=, ==, ===, !== |
| Unary Negation | const y = -x |
| Unary Plus | const x = +y |
| Property Accessor | person['name'] = 'Mirabel' |
Angular expressions additionally also support the following non-standard operators:
| Operator | Example(s) |
|---|---|
| Pipe | {{ total | currency }} |
| Optional chaining* | someObj.someProp?.nestedProp |
| Non-null assertion (TypeScript) | someObj!.someProp |
*Note: Optional chaining behaves differently from the standard JavaScript version in that if the left side of Angular’s optional chaining operator is null or undefined, it returns null instead of undefined.
Unsupported operators
| Operator | Example(s) |
|---|---|
| All bitwise operators | &, &=, ~, |=, ^=, etc. |
| Assignment operators | = |
| Object destructuring | const { name } = person |
| Array destructuring | const [firstItem] = items |
| Comma operator | x = (x++, x) |
| typeof | typeof 42 |
| void | void 1 |
| in | 'model' in car |
| instanceof | car instanceof Automobile |
| new | new Car() |
Lexical context for expressions
Angular expressions are evaluated within the context of the component class as well as any relevant template variables, locals, and globals.
When referring to class members, this is always implied.
Declarations
Generally speaking, declarations are not supported in Angular expressions. This includes, but is not limited to:
| Declarations | Example(s) |
|---|---|
| Variables | let label = 'abc', const item = 'apple' |
| Functions | function myCustomFunction() { } |
| Arrow Functions | () => { } |
| Classes | class Rectangle { } |
Event handlers are statements rather than expressions. While they support all of the same syntax as Angular expressions, the are two key differences:
- Statements do support assignment operators (but not destructing assignments)
- Statements do not support pipes