an-expression

anExpression lets you programmatically build JavaScript expressions, modify them, and then turn them into source code.

var anExpression = require("an-expression")
var javascriptToEzjs = require("javascript-to-ezjs")
 
var tree = anExpression.tree()
 
javascriptToEzjs("blah({\n  a: 1,})", tree)

Once we have built a tree, we can query the data. Here we'll iterate through the key value pairs on that object expression, and expect to see the number 1:

var objectExpressionId = tree.getListItem("arguments", tree.rootId(), 0)
 
tree.eachListItem(
  "pairIds",
  objectExpressionId,
  function(pairId) {
    var key = tree.getAttribute(tree, "key", pairId)
    var parentId = tree.getAttribute("key", pairId)
    var valueId = tree.getAttribute("valueId", pairId)
    var number = tree.getAttribute("number", valueId)
 
    if (number != 1) {
      throw new Error("Bad number") }
 
    if (parentId != tree.root().id) {
      throw new Error("Bad root")}})

We can also modify the tree:

tree.addKeyValuePair(
  objectExpressionId,
  "b",
  tree.numberLiteral(2))

And then dump the modified code:

// tree.toJavaScript() returns:
blah({
  a: 1,
  b: 2})

Methods

// Adds an empty function literal at the next available position
tree.addExpressionAt(
  tree.reservePosition(),
  anExpression.functionLiteral())
 
// Add a string literal inside that function literal
var functionId = tree.rootId()
var stringLiteral = anExpression.stringLiteral("alert")
tree.addToParent(functionId, stringLiteral)

Expression generators

 
var hello = anExpression.stringLiteral("hello, world")
 
// "hello, world"
 
anExpression.functionLiteral({
  functionName: "add",
  argumentNames: ["a", "b"],
  body: hello})
 
// function add(a, b) {
//   "hello, world"
// }
 
var a = anExpression.numberLiteral(42)
 
// 42
 
var b = anExpression.numberLiteral(1)
 
// 1
 
anExpression.functionCall({
  functionName: "add",
  arguments: [a, b]})
 
// add(42, 1)
 
anExpression.variableReference("a")
 
// a
 
anExpression.variableAssignment({
  variableName: "a",
  expression: "b"})
 
// a = b
 
anExpression.variableAssignment({
  variableName: "c",
  expression: "b",
  isDeclaration: true})
 
// var c = b
 
anExpression.objectLiteral({
  name: a.id
})
 
// {name: a}
 
anExpression.arrayLiteral([a.id, b.id])
 
// [a, b]
 
anExpression.boolean(true)
anExpression.true()
 
// true
 
anExpression.false()
 
// false
 
anExpression.returnStatement({
  expression: a})
 
// return a