svuelte

svuelte

This small script is intended to make transitioning from Vue to Svelte easier. Those frameworks are used in a similar fashion, but conceptually use quite different approaches (Vue is a more traditional one, a library, and Svelte is a "dissapearing framework").

Because of those similarities, it's possible to automate some of the changes. It doesn't mean that this tool will do everything for you — but it'll try. Some features of Vue are missing from Svelte; if you use them, you'll need to rewrite some parts of your components manually. In most cases, svuelte will point you to such parts.

For now, this tool only works on SFC (Single File Components) individually, converting .vue files to .svelte.

Installation and usage

npm install -g svuelte

This will make svuelte available globally. Now you can run it:

svuelte /path/to/some/vue/Component.vue /path/to/converted/svelte/Component.svelte

You can omit output path, in that case .svelte file will be produced in the current directory.

What svuelte will do

Convert script tag

Svuelte expects that your Vue component contains JS code with a single export default statement, containing a component declaration as a static object:

<script>
export default {
  name: 'AButton',
  ...
}
</script>

It will look into this object and convert following fields:

• props will be converted to export let prop = defaultValue; // type
• data will be converted to let field = initialValue;
• computed will be converted to $: computedField = (() => { ... })();. In case the compute function contains only a single return statement, it will become simply $: computedField = expressionAfterReturn;
• beforeCreated and created will be inlined after all variable declarations, at the top of generated script tag
• mounted, beforeUpdate, updated, destroyed hooks will be converted to appropriate Svelte equivalents (onMount, beforeUpdate, afterUpdate, onDestroy)
• methods will be converted to function declarations at the bottom of the generated script tag

Svuelte will try and remove this. from places where it would be bound to the component instance (it's not needed in Svelte, as all component fields available as local variables).

It will look into arrow functions (() => this.x * 2 will become () => x * 2), but won't touch simple function declarations (function foo() { return this.x; } will be left unchanged).

However, if you instantly bind a function to this, this binding will be removed as well as all references to this from within that function:

let bar = function() {
  console.log(this.x);
}.bind(this);

Will become:

let bar = function() {
  console.log(x);
}

Convert css sections

Any style block with a scoped attribute will be left unchanged (in Svelte all styles are scoped by default).

Within unscoped stylesheets, each rule will be wrapped in a :global(...) pseudo-selector.

Convert template

Svuelte will unwrap the <template> tag and put it contents and the bottom of the generated Svelte component.

It will perform following transformations:

• Attributes starting with v-bind: and : will be converted to attr="{boundValue}" syntax
• Attributes starting with v-on: and @ will be converted to on:event="{boundFunction}" syntax
• v-if, v-else-if, v-else and v-for directives will be converted to corresponding Svelte blocks ({#if ...}, {:else if ...}, {:else}, {#each ...})
• v-html directive will be converted to {@html field} (if element contained any children, they will be discarded)
• Double-bracket {{ interpolations }} will be transformed to {single-bracket}

What svuelte won't do

As you can see already, Svuelte does not cover all features of Vue. In particular,

• For now, Svuelte will silently ignore all references to special fields and methods available on Vue component instances (they start with a "$", like $set, $slots and so on)
• Directives v-text, v-show, v-slot, v-pre, v-cloak, v-once are silently ignored too (for now). Same applies for "special attributes" key, ref and is
• Vue built-in helper components (like <component>, <keep-alive>, <transition>) are not converted and left as-is
• Except for those mentioned above, none of the component options are supported (including render, watch, updated, activated, deactivated and so on). Svuelte will report each field it was unable to convert
• Svuelte does not support validation on component properties, unlike Vue. Because of that, the type of the property will be left only as a comment after its declaration. If your component contained custom validators, they will be discarded and Svuelte will warn you about that
• Computed fields with setters are not supported for now

Also Svuelte won't perform any improvements/optimisations on your code (except for the trivial ones, like removing this). Some parts are probably will be possible to rewrite in a more elegant way (computed fields, for example).

Once again, after you run svuelte, you'll probably get not working code. But it will hopefully help you to get started.