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.