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labels.spec.js

import assert from 'assert';

it('a label must be defined before its usage', () => {
  assert.throws(() => eval(`
    continue label0;
    label0;
  `)
  );
});

it('label followed by let throws', () => {
  assert.throws(() => eval(`
      label:
      let a1 = 1;
    `)
  );
});

it('label followed by var does not throw', () => {
  assert.doesNotThrow(() => eval(`
      label:
      var a1 = 1;
    `)
  );
});

it('label followed by const throws badly', () => {
  assert.throws(() => eval(`
      label:
      const a1 = 1;
    `)
  );
});

it('label followed by const inside the scope does not throw', () => {
  assert.doesNotThrow(() => eval(`
      label:
      { const a1 = 1; }
    `)
  );
});

it('label followed by let inside braces does not throw', () => {
  assert.doesNotThrow(() => eval(`
      label:{ let a1 = 1 }
    `)
  );
});

it('a function after a lable throws (spec 13.13.1)', () => {
  // https://tc39.github.io/ecma262/#sec-labelled-statements
  assert.throws(() => eval(`
      label:
      function f() {}
    `)
  );
});

it('a label can not be a number', () => {
  assert.throws(() => eval(`
      10:
      {}
    `)
  );
});

describe('dynamic labels? (can use variables for labels?)', () => {
  it('we cant use variables as labels', () => {
    assert.throws(() => eval(`
      const x = 'label';
      x:
      while(true){
        continue label;
      }
    `), SyntaxError);
  });
});

it('breaking to a certain label exits the block of the label', () => {
  bar: {
    while (true) {
      break bar;
    }
    assert(false);
  }
});
it('breaking inside a loop of a labeled block only exits the loop', () => {
  bar: {
    while (true) {
      break;
    }
    assert(true);
    return;
  }
  assert(false, 'It should not get here.');
});

it('`break` breaks out of any number of loops', () => {
  bar: 
  while (true) {
    while (true) {
      break bar;
    }
  }
});
it('continue', () => {
  let a = 0;
  bar: 
  while (a<1) {
    a+= 10;
    bar1:
    while (a<100) {
      continue bar;
    }
  }
  assert.equal(a, 10);
});

xit('succeeds if the label is defined in a while statement', () => {
  label1:
  {
    let a = 0;
    while(a < 2) {
        label2:
        {
          a++;
          break label1;
        }
    }
  }
  
  // for(var i=0;i<5;i++) {
  //   let a=0;
  //   if (a<2) {
  //     a=a+1;
  //     continue label1;
  //   } else {
  //     assert(false)
  //   }
  // }
});