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Web Storage API

Deno 1.10 introduced the Web Storage API which provides an API for storing string keys and values. Persisting data works similar to a browser, and has a 10MB storage limit. The global sessionStorage object only persists data for the current execution context, while localStorage persists data from execution to execution.

In a browser, localStorage persists data uniquely per origin (effectively the protocol plus hostname plus port). As of Deno 1.16, Deno has a set of rules to determine what is a unique storage location:

  • When using the --location flag, the origin for the location is used to uniquely store the data. That means a location of http://example.com/a.ts and http://example.com/b.ts and http://example.com:80/ would all share the same storage, but https://example.com/ would be different.
  • If there is no location specifier, but there is a --config configuration file specified, the absolute path to that configuration file is used. That means deno run --config deno.jsonc a.ts and deno run --config deno.jsonc b.ts would share the same storage, but deno run --config tsconfig.json a.ts would be different.
  • If there is no configuration or location specifier, Deno uses the absolute path to the main module to determine what storage is shared. The Deno REPL generates a "synthetic" main module that is based off the current working directory where deno is started from. This means that multiple invocations of the REPL from the same path will share the persisted localStorage data.

This means, unlike versions prior to 1.16, localStorage is always available in the main process.


The following snippet accesses the local storage bucket for the current origin and adds a data item to it using setItem().

localStorage.setItem("myDemo", "Deno App");

The syntax for reading the localStorage item is as follows:

const cat = localStorage.getItem("myDemo");

The syntax for removing the localStorage item is as follows:


The syntax for removing all the localStorage items is as follows: