JavaScript iteration
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This document discusses different types of loops in JavaScript including while, do-while, for, and for-in loops. It explains that while loops check a condition at the top of the loop, do-while loops check at the bottom to ensure the code block runs at least once, and basic for loops allow controlling the number of loop iterations with initialization, condition, and preparation statements. The document also covers using for-in loops to examine object properties and the importance of filtering with hasOwnProperty to avoid inherited properties, as well as how to exit loops early with break or continue.
JavaScript iteration
- 2. Changes in Direction ● In the previous video we allowed our program to change flow to one of many different program blocks ● But that is not the only direction change we may want. It is often desireable to repeatedly execute the same block ● Looking for some value in a list ● Sending a group email ● In other words we want to loop
- 3. The While loop ● At the top of the loop the condition is checked ● If the condition is met then execute code block ● Loop will continue until condition not met. while (conditional expression) { //Do some stuff } ● Be sure that eventually the condition will not be met otherwise you get an infinite loop;
- 4. The Do loop ● At the bottom of the loop condition is checked ● Assures the code block will be executed at least once ● Loop continues until condition false do { //code to execute goes here } while (conditional expression);
- 5. Basic For loop ● Executes the loop a number of times ● Has three statements ● First excutes before the loop is executed – Usually used for initialization ● Second conditional expression – Code executes if true ● Third – Executes after the code block before the next iteration
- 6. Basic For Syntax for (init ; conditional exp; prepForNext) { //do some stuff }
- 7. For looping through properties ● Used to examine properties of an object ● Important to filter as all properties examined even those inherited from parent and its parent.... for (variable in Object) { if ( Object.hasOwnProperty(variable) { //code to execute } }
- 8. Cutting the loop ● break ● Halts code execution in the loop – Stop further execution of code block and exit the loop ● continue ● Halts execution of the rest of the code block ● Continues next iteration
- 9. Summary ● Iteration is another word for looping ● While loops check for conditional at the top of the loop ● Be wary of the infinite loop ● Do loops check conditional at bottom of the loop ● Basic for loops allow loops to be controlled by number of executions ● For in loops will check properties of Objects and Arrays ● Be sure to use hasOwnProperty method.
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