Some of the ilib packages supported node 10 through the current latest version and used jest as their unit testing library. The only problem is that the latest version of jest did not run on node 10 through 13 because it was rewritten with ES6 syntax in jest@27.0.0. The tests, which were not particularly fancy and did not use any advanced features, ran fine with jest@26.6.2 on older versions of node but would not work with the latest jest because it wasn't transpiled to support older versions of node.

What was needed was a way to install jest@26 for older versions of node and jest@29 for the newer ones. There was no easy, elegant way to do that.

Hence this conditional install package.

How Does it Work?

Usage is simple. Basically, modify your package.json to include conditional dependencies, and then run this package as a postinstall script.

Here is what the package.json would look like:

{
    "name": "mypackage",
    "scripts": {
        "postinstall": "conditional-install"
    },
    "dependencies": {
        "conditional-install": "^1.0.0"
    },
    "conditionalDependencies": {
        "process.version >= 14.0.0": {
            "example-package": "^29.0.0"
        },
        "process.version < 14.0.0": {
            "example-package": "^26.0.0"
        }
    }
}

The postinstall script is run automatically by npm or yarn after the regular installation is complete. If you are using npm-ci, it does not, so you will have to run npm-ci run postinstall explicitly in order to install the conditional dependencies.

The conditionalDependencies object contains properties that are expressions to test against the current version of node. Inside of the value object is a list of dependencies to install if the value of that expression is true. All dependencies inside of the value are installed. The versions are specified with the same syntax as regular, dev, or peer dependencies.

When the dependencies are installed, they are installed using the current package manner, but in such a way that the new dependencies are not saved to the package.json.

Conditional Expressions

The expressions are built on the hard work of node-compat-table.

The core of an expression is a test. There are multiple things that can be tested:

A JS "feature" to test against from the node-compat-table project. This tests whether or not the current version of node supports that feature. For example, the feature may be RegExp.prototype.flags. See the node.green web site to see all the possible features and their pass/fail values for various versions of node.
ECMAScript versions. If you give then name or alias of a version of ECMAScript, it can test to see if the current version of node supports that form of ECMAScript. Examples are "ES2015" or "ES6" or "ESM". The data for this is also from node-compat-tables.
The value of a setting in the process variable. There are various different possible types of values:
- numbers. Example: process.config.variables.icu_ver_major will give you the major version of ICU that this version of node supports as a number
- strings. Example: process.ENV.variableName will return you the value of an environment variable as a string. In this way, you can control conditional installation with external means. Strings may have spaces and other characters in them so that they can represent JS features.
- versions. Example: process.versions.node will return a full version spec, like "v14.4.2" or "18.0.0". This may or may not have the leading "v" in front of it.
- booleans. Example: process.config.variables.icu_small return true if this version of node uses the small ICU package, and false if this version has full ICU.

Individual tests can be combined into more complex expressions together using the following familiar operators. All operators return a boolean value as well.

! is "not". A value can be negated using this unary operator, meaning that the current version of node does NOT support that feature. Negation for numbers are similar to Javascript's truthy and falsy. String literals that do not name a JS feature, an ES version, or a setting inside of the process variable are considered to be false.
&& is "and". Both sides must be true
|| is "or". At least one side must be true
= is "equals". Both sides must be equal
!= is "not equal". Both sides must not be equal each other
> is "greater than". Left side must be greater than the right side
>= is "greater than or equal to". Left side must be greater than or equal to the right side
< is "less than". Left side must be less than the right side
<= is "less than or equal to". Left side must be less than or equal to the right side.
^ is "major compatibility". For versions, this is the same as carat compatibility in the semver package. For strings and numbers, this operator returns false.
~ is "minor compatibility". For versions, this is the same as tilde compatibility in the semver package. For strings and numbers, this operator returns false.
- is "range". For versions, this is the range operator which forms ranges of versions. For strings and numbers, this operator returns false.
( and ) group expressions together to enforce order of operations

When the two sides of a binary operator are versions, this package will use semver to compare them using all the normal, familiar semver rules. Examples:

"process.versions.node ^ 14.0.0" -> test whether or not the current version of node
is carat compatible with version 14.0.0

"process.versions.node < v14.0.0" -> test whether or not the current version of node
is less than version 14.0.0

If the two sides of an operator are different types, the right side will be co-ersed to the same type as the left side. - strings become numbers with parseInt() - numbers become boolean with 0 = false, any other number = true - numbers become versions by treating them as a major version number. 14 = v14.0.0 - strings become booleans by value. "true" is true, and everything else is false

Example of a conditional expression using more complex syntax:

    "conditionalDependencies": {
        "!ES6 || (process.config.variables.icu_ver_major < 67 && process.config.variables.icu_small)": {
            "full-icu": "^1.5.0"
        }
    }

Conditional Dev Dependencies

If you put "conditional-install" into the postinstall script, both npm and yarn will run the conditional installation whether you are doing npm install locally in your cloned git repo, or including your package into another package from the npm repository.

In some cases, you only want to do conditional installation when running locally during development. To do that, put "conditional-install" into the "prepare" script instead and include "conditional-install" in your devDependencies instead:

{
    "name": "mypackage",
    "scripts": {
        "prepare": "conditional-install"
    },
    "devDependencies": {
        "conditional-install": "^1.0.0"
    },
    "conditionalDependencies": {
        "process.version >= 14.0.0": {
            "jest": "^29.0.0"
        },
        "process.version < 14.0.0": {
            "jest": "^26.0.0"
        }
    }
}

License

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

See the License for the specific language governing permissions and limitations under the License.

Release Notes

v1.0.2

now while installing the conditional dependencies, it ignores any automatically run scripts you may have set up in your package.json . The original run of npm install will run those scripts properly once the conditional install is complete. This prevents a recursive install loop.
tests now run properly on node 22

v1.0.1

fixed a broken "postinstall" script in the package.json
updated documentation

v1.0.0

Initial version

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Package last updated on 08 Oct 2024

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