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0.1.0 • Public • Published


This TypeScript custom transform will transform expressions that use a safely keyword/call to produce safe property access and modification.


$ npm install ts-transform-safely

And then put this in your list of before transformers when you compile TS. If you are using webpack/ts-loader, this is a simple addition to your ts-loader config:

// webpack.config.js:
const safelyTransformer = require('ts-transform-safely').default
// exports.module.rules[]
      test: /\.ts$/,
      loader: 'ts-loader',
      options: {
          getCustomTransformers: () => ({
              before: [safelyTransformer()]
          transpileOnly: true

Otherwise you will need to use the TypeScript compiler API to load the transform.


The basic format of using the transform is to write object-checked, safe expressions (existential property access) in the form:


We can include a reference to ts-transform-safely/typings.d.ts, in your tsconfig.json or as a comment reference, to ensure that safely is declared/typed:

/// <reference path="../../typings.d.ts" />

We can then access properties on variables that may be set to null or undefined, and they won't error out. For example:

safely(object.subObject.subProperty) // will check for each object's existence before accessing property

Will be rewritten to:

var _object
(_object = object == null ? void 0 : object.subObject) == null ? void 0 : _object.subProperty

So if object or subObject is not an object, the entire expression will return undefined (without an error).

And we can assign properties to objects thay may not exist yet, and they will be created:

safely(object.subObject.subProperty = 4) // will create the any missing objects in order to assign property

If object or subObject are not objects, they will be assigned an object.

And we can make function or method calls on functions may or may not exist as well:

safely(object.method(args)) // will only call if method exists

Again, this will return undefined if the method doesn't exist.

If you use a numeric index or the push or unshift method, the code will be transformed to create an array as necessary (rather than just doing an existence check). For example:


If arrayProperty is not defined, an array will be created (and push called on it).

And of course you can combine any permutation of the above (with any other valid expression or operator):

safely(empty.b.c = object[a]() || object[b](something.c.d))

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npm i ts-transform-safely

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