@babel/template

When calling template as a function with a string argument, you can provide placeholders which will get substituted when the template is used.

You can use two different kinds of placeholders: syntactic placeholders (e.g. %%name%%) or identifier placeholders (e.g. NAME). @babel/template supports both those approaches by default, but they can’t be mixed. If you need to be explicit about what syntax you are using, you can use the syntacticPlaceholders option.

Please note that syntactic placeholders were introduced in Babel 7.4.0. If you don’t control the @babel/template version (for example, when importing it from a @babel/core@^7.0.0 peer dependency), you must use identifier placeholders. On the other hand, syntactic placeholders have some advantages: they can be used where identifiers would be a syntax error (e.g. in place of function bodies, or in export declarations), and they don’t conflict with uppercase variables (e.g., new URL()).

Input (syntactic placeholders):

import template from "@babel/template";
import generate from "@babel/generator";
import * as t from "@babel/types";
const buildRequire = template(`
  var %%importName%% = require(%%source%%);
`);
const ast = buildRequire({
  importName: t.identifier("myModule"),
  source: t.stringLiteral("my-module"),
});
console.log(generate(ast).code);

Input (identifier placeholders):

Output:

If no placeholders are in use and you just want a simple way to parse a string into an AST, you can use the version of the template.

which will parse and return the AST directly.

import template from "@babel/template";
import generate from "@babel/generator";
import * as t from "@babel/types";
const source = "my-module";
const fn = template`
  var IMPORT_NAME = require('${source}');
`;
const ast = fn({
  IMPORT_NAME: t.identifier("myModule"),
});
console.log(generate(ast).code);

Note that placeholders can be passed directly as part of the template literal in order to make things as readable as possible, or they can be passed into the template function.

.ast

If no placeholders are in use and you just want a simple way to parse a string into an AST, you can use the .ast version of the template.

The @babel/template API exposes a few flexible APIs to make it as easy as possible to create ASTs with an expected structure. Each of these also has the .ast property mentioned above.

template

template returns either a single statement, or an array of statements, depending on the parsed result.

This is the same as the default template API, returning either a single node, or an array of nodes, depending on the parsed result.

template.statement

template.statement("foo;")() returns a single statement node, and throw an exception if the result is anything but a single statement.

template.statements

template.statements("foo;foo;")() returns an array of statement nodes.

template.expression("foo")() returns the expression node.

template.program

template.program("foo;")() returns the node for the template.

template(code, [opts])

code

Type: string

options

@babel/template accepts all of the options from , and specifies some defaults of its own:

• allowReturnOutsideFunction is set to true by default.
• allowSuperOutsideMethod is set to true by default.

syntacticPlaceholders

Type: boolean Default: true if %%foo%%-style placeholders are used; false otherwise. Added in: v7.4.0

placeholderWhitelist

Type: Set<string> Default: undefined

A set of placeholder names to automatically accept. Items in this list do not need to match the given placeholder pattern.

placeholderPattern

Type: RegExp | false Default: /^[_$A-Z0-9]+$/

This option is not compatible with syntacticPlaceholders: true

A pattern to search for when looking for Identifier and StringLiteral nodes that should be considered placeholders. ‘false’ will disable placeholder searching entirely, leaving only the ‘placeholderWhitelist’ value to find placeholders.

preserveComments

Type: boolean Default: false

Set this to true to preserve any comments from the code parameter.

Return value

By default @babel/template returns a function which is invoked with an optional object of replacements. See the usage section for an example.

When using , the AST will be returned directly.