simple-json-template

A Simple JSON template engine to render JSON structured data

Example

docker-compose Template (yaml)

version: '3',
services: 
  '~~~for': 'services as (service, i)'
  '${service.name}':
    image: 'myrepo/${service.name}:${service.version}'
    build:
      context: '${service.name}'
      dockerfile: '${service.name}/Dockerfile'
    ports:
      '~~~for': 'service.ports as (containerPort, j)'
      '~~~each': '${9000 + j + (i * 10)}:${containerPort}'
    'environment':
      '~~~for': 'service.envs as env'
      '${env.name}': '${env.value}'

Data (json)

{
  "services": [
    {
      "name": "order-service",
      "version": "1.0",
      "ports": [ 8080 ],
      "envs": [
        {
          "name": "product_service_url",
          "value": "http://product-service:8080"
        }
      ]
    },
    {
      "name": "product-service",
      "version": "3.5",
      "ports": [ 8080, 9001 ],
      "envs": [
        {
          "name": "database_host",
          "value": "mysql.hosts"
        },
        {
          "name": "database_name",
          "value": "product-database"
        },
        {
          "name": "database_username",
          "value": "product-database"
        },
        {
          "name": "database_password",
          "value": "mypass123"
        }
      ]
    }
  ]
}

Output (yaml)

version: '3',
services: 
  order-service:
    image: 'myrepo/order-service:1.0'
    build:
      context: .
      dockerfile: 'order-service/Dockerfile'
    ports:
      - '9000:8080'
    environment:
      product_service_url: 'http://product-service:8080'
  product-service:
    image: 'myrepo/product-service:3.5'
    build:
      context: .
      dockerfile: 'product-service/Dockerfile'
    ports:
      - '9010:8080'
      - '9011:9001'
    environment:
      database_host: 'mysql.hosts'
      database_name: 'product-database'
      database_username: 'product-database'
      database_password: 'mypass123'
     

Install

npm install simple-json-template

Usage

var TemplateEngine = require("simple-json-template");

var result = TemplateEngine.render({
  say: "${message}"
}, {
  message: "Hello!"
});

Syntax

A Simple JSON Template is basically an object structure which describes how it should be rendered based on input data. The template can be defined in JSON, Yaml or in Javascript itself.

Expressions

Expressions are a string of JavaScript code to get data or manipulate it. For example: ${myList.length}. Or a more complicated expression: ${myList.filter(item => !item.hidden).map(item => item.name).join(', ')}. The JavaScript code is executed in a sandbox provided by vm2

Variables

You can use variables inside an expression. These variables can be provided when rendering the template:

var result = TemplateEngine.render({
  say: "${message}"
}, {
  message: "Hello!"
});
// 'say' renders as "Hello!"

Variables can also be found in the template itself:

var result = TemplateEngine.render({
  message: "Hello",
  output: {
    name: "Bill!",
    say: "${_root.message} ${_this.name}"
  }
});
// 'output.say' renders as "Hello Bill!"

The variable _this returns the current object where the expression is and the _root variable returns the root object of the template.

~~~if Statement

The if statement can be used to show parts of template based on a condition.

Example 1: if statement is true

var result = TemplateEngine.render({
  user: {
    name: "Bob"  
  },
  '~~~if': "_this.user.toLowerCase() === 'bob'"
});
// renders as:
// {
//   user: {
//     name: "Bob",
//   }
// }

Example 2: if statement is false

var result = TemplateEngine.render({
  user: {
    name: "John"  
  },
  '~~~if': "_this.user.toLowerCase() === 'bob'"
});
// renders as:
// {}

Example 3: if statement with then

var result = TemplateEngine.render({
  user: {
    name: "Bob"  
  },
  '~~~if': "_this.user.toLowerCase() === 'bob'",
  '~~~then': {
    user: {
      name: "Bob Awesome!"
    }
  }
});
// renders as:
// {
//   user: {
//     name: "Bob Awesome!",
//   }
// }

Example 4: if statement with else

var result = TemplateEngine.render({
  user: {
    name: "John"  
  },
  '~~~if': "_this.user.toLowerCase() === 'bob'",
  '~~~else': {
    user: {
      name: "Not Bob"
    }
  }
});
// renders as:
// {
//   user: {
//     name: "Not Bob",
//   }
// }

~~~for Statement

The for statement can be used for looping over a list.

Example 1: loop over list

var result = TemplateEngine.render({
  user: {
    '~~~for': "users as user",
    name: "${user}"
  }
}, {
  users: ["Bob", "Alise"]
});
// renders as:
// {
//   users: [
//     {
//       name: "Bob",
//     },
//     {
//       name: "Alise",
//     }]
// }

Example 2: use index and length

var result = TemplateEngine.render({
  user: {
    '~~~for': "users as (user, index, length)",
    id: "${index}/${length}",
    name: "${user}"
  }
}, {
  users: ["Bob", "Alise"]
});
// renders as:
// {
//   users: [
//     {
//       id: "0/2"
//       name: "Bob",
//     },
//     {
//       id: "1/2"
//       name: "Alise",
//     }]
// }

Example 3: loop using each

var result = TemplateEngine.render({
  user: {
    '~~~for': "users as user",
    '~~~each': {
      name: "${user}"
    }
  }
}, {
  users: ["Bob", "Alise"]
});
// renders as:
// {
//   users: [
//     {
//       name: "Bob",
//     },
//     {
//       name: "Alise",
//     }]
// }

Example 4: loop using property keys

var result = TemplateEngine.render({
  user: {
    '~~~for': "users as user, id",
    '${user}': {
      id: "${id}"
    }
  }
}, {
  users: ["Bob", "Alise"]
});
// renders as:
// {
//   users: {
//     Bob: {
//       id: "0"
//     },
//     Alise: {
//       id: "1",
//     }
//   }
// }

Licence

MIT