babel/packages/babel-traverse/test/evaluation.js

import traverse from "../lib";
import assert from "assert";
import { parse } from "babylon";

function getPath(code) {
  const ast = parse(code);
  let path;
  traverse(ast, {
    Program: function (_path) {
      path = _path;
      _path.stop();
    },
  });
  return path;
}

describe("evaluation", function () {
  describe("evaluateTruthy", function () {
    it("it should work with null", function () {
      assert.strictEqual(
        getPath("false || a.length === 0;").get("body")[0].evaluateTruthy(),
        undefined
      );
    });

    it("it should not mistake lack of confidence for falsy", function () {
      assert.strictEqual(
        getPath("foo || 'bar'").get("body")[0].evaluate().value,
        undefined
      );
    });
  });

  it("should bail out on recursive evaluation", function () {
    assert.strictEqual(
      getPath("function fn(a) { var g = a ? 1 : 2, a = g * this.foo; }")
        .get("body.0.body.body.0.declarations.1.init").evaluate().confident,
      false
    );
  });

  it("should work with repeated, indeterminate identifiers", function () {
    assert.strictEqual(
      getPath("var num = foo(); (num > 0 && num < 100);").get("body")[1].evaluateTruthy(),
      undefined
    );
  });

  it("should work with repeated, determinate identifiers", function () {
    assert.strictEqual(
      getPath("var num = 5; (num > 0 && num < 100);").get("body")[1].evaluateTruthy(),
      true
    );
  });

  it("should deopt when var is redeclared in the same scope", function () {
    assert.strictEqual(
      getPath("var x = 2; var y = x + 2; { var x = 3 }")
        .get("body.1.declarations.0.init").evaluate().confident,
      false
    );
  });

  it("it should not deopt vars in different scope", function () {
    const input = "var a = 5; function x() { var a = 5; var b = a + 1; } var b = a + 2";
    assert.strictEqual(
      getPath(input).get("body.1.body.body.1.declarations.0.init").evaluate().value,
      6
    );
    assert.strictEqual(
      getPath(input).get("body.2.declarations.0.init").evaluate().value,
      7
    );
  });

  it("it should not deopt let/const inside blocks", function () {
    assert.strictEqual(
      getPath("let x = 5; { let x = 1; } let y = x + 5")
        .get("body.2.declarations.0.init").evaluate().value,
      10
    );
    const constExample = "const d = true; if (d && true || false) { const d = false; d && 5; }";
    assert.strictEqual(
      getPath(constExample).get("body.1.test").evaluate().value,
      true
    );
    assert.strictEqual(
      getPath(constExample).get("body.1.consequent.body.1").evaluate().value,
      false
    );
  });

  it("should deopt ids that are referenced before the bindings", function () {
    assert.strictEqual(
      getPath("let x = y + 5; let y = 5;").get("body.0.declarations.0.init").evaluate().confident,
      false
    );
    assert.strictEqual(
      getPath("if (typeof x === 'undefined') var x = {}")
        .get("body.0.test").evaluate().confident,
      false
    );
  });

  it("should evaluate undefined, NaN and Infinity", () => {
    assert.strictEqual(getPath("undefined").get("body.0.expression").evaluate().confident, true);
    assert.strictEqual(getPath("NaN").get("body.0.expression").evaluate().confident, true);
    assert.strictEqual(getPath("Infinity").get("body.0.expression").evaluate().confident, true);
  });

  it("should deopt redefined primitives - undefined, NaN and Infinity", () => {
    const eval_undef = getPath("let undefined; undefined;").get("body.1.expression").evaluate();
    const eval_nan = getPath("let NaN; NaN;").get("body.1.expression").evaluate();
    const eval_inf = getPath("let Infinity; Infinity;").get("body.1.expression").evaluate();
    assert.strictEqual(eval_undef.confident, false);
    assert.strictEqual(eval_nan.confident, false);
    assert.strictEqual(eval_inf.confident, false);

    assert.strictEqual(eval_undef.deopt.type, "VariableDeclarator");
    assert.strictEqual(eval_undef.deopt.parentPath.node.kind, "let");
  });
});