"use strict"; {

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Summary

This module is here to tell you to use "use strict";!

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Contents

• "use strict";

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"use strict";

In this class we will include the "use strict"; directive at the top of our .js files (unless they define a class).

"use strict"; will turn on special rules that will help us to find errors in our code more easily. In reality, it mostly comes down to one rule: it won’t let us use variable we haven’t explicitly declared.

This is helpful because it lets us avoid deeply frustrating bugs that occur when we accidentally create a new variable instead of assigning to an existing one, usually thanks to a typo:

Without "use strict";

let circleWidth;
let circleHeight;

circleWitdh = 50; // This generates a NEW VARIABLE called circleWitdh and assigns it 50
circleHeight = 50;

// This won't work as expected because circleWidth is STILL undefined (we assigned 50 to
// circleWitdh, not circleWidth)
ellipse(0,0,circleWidth,circleHeight);

Our circle won’t be drawn, because circleWidth is undefined, but we won’t see any errors! This makes it hard to see what went wrong, especially if this were a larger program.

With "use strict";

"use strict";

function setup() {
  let circleWidth;
  let circleHeight;

  circleWitdh = 50; // This will be an ERROR in the console
  circleHeight = 50;

  ellipse(0,0,circleWidth,circleHeight);
}

Our circle won’t be drawn, still, but now we will see an error message in the console:

ReferenceError: circleWitdh is not defined

That error then helps us to see our mistake! Phew!

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Use "use strict";!

It is your friend and it wants to help you.

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}