p5.js constrain() Function

Last Updated : 12 Jul, 2025
The constrain() function in p5.js is used to constrain a number between a given minimum and maximum limit. Syntax: 
constrain( n, low, high )
Parameters: This function accept three parameters as mentioned above and described below:
  • n: It is a number which denotes the value that has to be constrained.
  • low: It is a number which denotes the minimum limit to which the number is constrained.
  • high: It is a number which denotes the maximum limit to which the number is constrained.
Return Value: It returns a number with the constrained value. The example below illustrates the constrain() function in p5.js: Example 1: javascript 
function setup() {
  createCanvas(650, 200);
  textSize(20);
 
  inputElemA = createInput(10);
  inputElemA.position(30, 40);
 
  inputElemB = createInput(100);
  inputElemB.position(30, 60);
 
  sliderElem = createSlider(-100, 100, 50, 1);
  sliderElem.position(30, 120);
}
 
function draw() {
  clear();
  text("Enter two values between which the "
    + "number would be constrained", 20, 20);
  text("Move the slider to observe the effects"
    + " of the constrain() function", 20, 100);
 
  // Convert the string value to a number value
  inputValA = Number(inputElemA.value());
  inputValB = Number(inputElemB.value());
  sliderVal = sliderElem.value();
 
  text("The slider value is: " + sliderVal, 20, 160);
 
  // Display the constrained value
  text("The constrained value is: "
        + constrain(sliderVal, inputValA,
        inputValB), 20, 180);
}
Output: constrain-slider Example 2: javascript 
function setup() {
  createCanvas(600, 350);
  textSize(20);
 
}
 
function draw() {
  clear();
  text("Move the pointer to see the effect "
        + "of constrain() in the square", 20, 30);
  text("White circle represents unconstrained"
        + " mouse", 20, 50);
  text("Red circle represents mouse constrained"
        + " to box dimensions", 20, 70);
 
  noFill();
  square(100, 100, 200);
 
  circle(mouseX, mouseY, 40);
 
  // Constrain the mouse x and y position
  constrainedMouseX = constrain(mouseX, 100, 300);
  constrainedMouseY = constrain(mouseY, 100, 300);
 
  fill('red');
  circle(constrainedMouseX, constrainedMouseY, 20);
}
Output: constrain-box-dimensions Online editor: https://editor.p5js.org/ Environment Setup: https://www.geeksforgeeks.org/javascript/p5-js-soundfile-object-installation-and-methods/ Reference: https://p5js.org/reference/#/p5/constrain
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