import declarations can only be present in modules, and only at the top-level (i.e. not inside blocks, functions, etc.). If an import declaration is encountered in non-module contexts (for example, tags without type="module", eval, new Function, which all have "script" or "function body" as parsing goals), a SyntaxError is thrown. To load modules in non-module contexts, use the dynamic import syntax instead.

import declarations are designed to be syntactically rigid (for example, only string literal specifiers, only permitted at the top-level, all bindings must be identifiers), which allows modules to be statically analyzed and linked before getting evaluated. This is the key to making modules asynchronous by nature, powering features like top-level await.

There are four forms of import declarations:

Below are examples to clarify the syntax.