jmespath

What is jmespath?

The jmespath npm package is a query language for JSON, allowing you to extract and manipulate data from complex JSON structures with ease. It provides a powerful and expressive syntax for querying and transforming JSON data.

What are jmespath's main functionalities?

Searching JSON data

This feature allows you to search through JSON data using JMESPath expressions. In this example, it searches for names of locations in the state of WA.

"search(jsonData, 'locations[?state == \"WA\"].name')"

Projection

Projection is used to extract a list of values from a JSON structure. This code sample demonstrates how to get a list of all location names.

"search(jsonData, 'locations[*].name')"

Functions

JMESPath supports a variety of functions to manipulate and transform data. This example uses the `length` function to count the number of locations.

"search(jsonData, 'length(locations)')"

Other packages similar to jmespath

lodash

Lodash is a utility library that provides functions for common programming tasks, including data manipulation. While it doesn't use a query language like JMESPath, it offers a wide range of methods for manipulating objects and arrays, making it a versatile alternative.

jsonpath

JsonPath is another query language for JSON, similar to JMESPath. It allows you to extract parts of a JSON document using a query syntax. While both aim to simplify data extraction from JSON, their syntax and capabilities differ, with JMESPath generally offering a more expressive query language.

README

jmespath.js

jmespath.js is a javascript implementation of JMESPath, which is a query language for JSON. It will take a JSON document and transform it into another JSON document through a JMESPath expression.

Using jmespath.js is really easy. There's a single function you use, jmespath.search:

> var jmespath = require('jmespath');
> jmespath.search({foo: {bar: {baz: [0, 1, 2, 3, 4]}}}, "foo.bar.baz[2]")
2

In the example we gave the search function input data of {foo: {bar: {baz: [0, 1, 2, 3, 4]}}} as well as the JMESPath expression foo.bar.baz[2], and the search function evaluated the expression against the input data to produce the result 2.

The JMESPath language can do a lot more than select an element from a list. Here are a few more examples:

> jmespath.search({foo: {bar: {baz: [0, 1, 2, 3, 4]}}}, "foo.bar")
{ baz: [ 0, 1, 2, 3, 4 ] }

> jmespath.search({"foo": [{"first": "a", "last": "b"},
                           {"first": "c", "last": "d"}]},
                  "foo[*].first")
[ 'a', 'c' ]

> jmespath.search({"foo": [{"age": 20}, {"age": 25},
                           {"age": 30}, {"age": 35},
                           {"age": 40}]},
                  "foo[?age > `30`]")
[ { age: 35 }, { age: 40 } ]

More Resources

The example above only show a small amount of what a JMESPath expression can do. If you want to take a tour of the language, the best place to go is the JMESPath Tutorial.

One of the best things about JMESPath is that it is implemented in many different programming languages including python, ruby, php, lua, etc. To see a complete list of libraries, check out the JMESPath libraries page.

And finally, the full JMESPath specification can be found on the JMESPath site.