graphql/language/lexing

Classes

Lexer

Given a Source object, creates a Lexer for that source. A Lexer is a stateful stream generator in that every time it is advanced, it returns the next token in the Source. Assuming the source lexes, the final Token emitted by the lexer will be of kind EOF, after which the lexer will repeatedly return the same EOF token whenever called.

Constructor

Creates a Lexer instance.

Signature:

new Lexer(source: Source)

Arguments

Name	Type	Description
source	`Source`	Source document used to derive error locations.

Returns

Type	Description
`Lexer`

Members

Name	Type	Description
source	`Source`	Source document used to derive error locations.
lastToken	`Token`	Most recent non-ignored token returned by the lexer.
token	`Token`	Current non-ignored token at the lexer cursor.
line	`number`	The (1-indexed) line containing the current token.
lineStart	`number`	Character offset where the current line starts.

advance()

Advances the token stream to the next non-ignored token.

Signature:

advance(): Token

Returns

Type	Description
`Token`	The next non-ignored token.

Example

import { Lexer, Source } from 'graphql/language';
 
const lexer = new Lexer(new Source('{ hello }'));
const token = lexer.advance();
 
// token.kind: '{'

lookahead()

Looks ahead and returns the next non-ignored token, but does not change the state of Lexer.

Signature:

lookahead(): Token

Returns

Type	Description
`Token`	The next non-ignored token without advancing the lexer.

Example

import { Lexer, Source } from 'graphql/language';
 
const lexer = new Lexer(new Source('{ hello }'));
const token = lexer.lookahead();
 
// token.kind: '{'

Enumerations

TokenKind

An exported enum describing the different kinds of tokens that the lexer emits.

Members

Name	Value	Description
`SOF`	`"<SOF>"`	Start-of-file token.
`EOF`	`"<EOF>"`	End-of-file token.
`BANG`	`"!"`	The `!` punctuation token.
`DOLLAR`	`"$"`	The `$` punctuation token.
`AMP`	`"&"`	The `&` punctuation token.
`PAREN_L`	`"("`	The `(` punctuation token.
`PAREN_R`	`")"`	The `)` punctuation token.
`DOT`	`"."`	The `.` punctuation token.
`SPREAD`	`"..."`	The `...` spread punctuation token.
`COLON`	`":"`	The `:` punctuation token.
`EQUALS`	`"="`	The `=` punctuation token.
`AT`	`"@"`	The `@` punctuation token.
`BRACKET_L`	`"["`	The `[` punctuation token.
`BRACKET_R`	`"]"`	The `]` punctuation token.
`BRACE_L`	`"{"`	The `{` punctuation token.
`PIPE`	`"\|"`	The `\|` punctuation token.
`BRACE_R`	`"}"`	The `}` punctuation token.
`NAME`	`"Name"`	A GraphQL name token or name AST node.
`INT`	`"Int"`	An integer value token or AST node.
`FLOAT`	`"Float"`	A floating-point value token or AST node.
`STRING`	`"String"`	A string value token or AST node.
`BLOCK_STRING`	`"BlockString"`	A block string value token.
`COMMENT`	`"Comment"`	A comment token.

Types

TokenKindEnum

Type alias. Deprecated in v16

Legacy alias for the enum type representing token kind values. This is retained for backwards compatibility; use TokenKind instead because TokenKindEnum will be removed in v17.

type TokenKindEnum = typeof TokenKind;

Kinds Parsing