Простое назначение переменных часов Javascript - PullRequest
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Простое назначение переменных часов Javascript

0 голосов
/ 16 апреля 2019

Следующий аннотированный код javascript создает простой таймер, который появляется в журнале консоли ради MWE.Я пытаюсь объяснить каждый бит этого кода, но я застрял на деталях назначения в разделах 2 и 10. Я смиренно прошу помочь заполнить недостающие фрагменты. 

//1-Create a function "startTimer" with parameter "duration"
function startTimer(duration) {

//2-Declare a variable "timer" with some strange comma separated assignment (HELP HERE)
var timer = duration, minutes, seconds;

//3-Declare an unassigned variable "output"
var output;

//4-setInterval, which has the syntax *setInterval(function, milliseconds, param1, param2, ...)* indicated that the code below will be performed every interval of 1000 ms, or every one second.
setInterval(function () {

//5-Assign variable "minutes" the value of timer/60 and has radix (base) 10.
minutes = parseInt(timer / 60, 10);

//6-Assign variable "seconds" the value of timer mod 60 and has radix (base) 10.
seconds = parseInt(timer % 60, 10);

//7-Assign variable "minutes" to the value of "0" + minutes if minutes < 10, or minutes if not. This is accomplished with the ternary operator "?", which has syntax *condition ? exprT : exprF* 
minutes = minutes < 10 ? "0" + minutes : minutes;

//8-Assign variable "seconds" in the same way minutes are assigned, which adds a leading zero if the value is <10.
seconds = seconds < 10 ? "0" + seconds : seconds;

//9-Assign variable "output" to minutes concatenated with ":" concatenated with seconds
output = minutes + ":" + seconds;

//10-If the value of timer incremented downward by one (HELP ON WHAT THAT MEANS) is less than zero then assign variable "timer" to the value of variable "duration", which will be (HELP ON WHERE DURATION GETS ITS VALUE).
if (--timer < 0) {
timer = duration;
}

//11-Output the formatted timer to the console log
console.log(output);

//12-End the function performed in setInterval. Also set the interval in which the function is repeated to 1000 ms (the second argument in the setInterval function).
}, 1000);

//13-End of function startTimer
}

Ответы [ 2 ]

2 голосов
/ 16 апреля 2019

Раздел 2 

var timer = duration, minutes, seconds;

В этой строке объявляются 3 переменные: timer, minutes и seconds.
Он также инициализирует переменную timer значением duration.

Раздел 10 

if (--timer < 0) {
timer = duration;
}

Синтаксис --timer означает, что значение таймера уменьшается на 1 сначала , а затем его значение считывается для сравнения if (timer < 0).
Переменная duration является аргументом функции startTimer, поэтому ее значение назначается за пределами этого кода пользователем функции.

0 голосов
/ 16 апреля 2019

Для полноты картины это обновленная версия с полными пояснениями. Этот код работает полностью в javascript и без HTML и т. Д. (Например, в студии приложений code.org). 

//1-Create a function "startTimer" with parameter "duration"
function startTimer(duration) {

//2-Declare a variable "timer" and assign it the value of the parameter "duration".
var timer = duration;


//3-Declare unassigned variables "output", "minutes", and "seconds".
var output;
var minutes;
var seconds;

//4-setInterval, which has the syntax *setInterval(function, milliseconds, param1, param2, ...)*. With section 12, this code below will be performed every interval of 1000 ms, or every one second.
setInterval(function () {

//5-Assign variable "minutes" the value of timer/60 with radix (base) 10.
minutes = parseInt(timer / 60, 10);

//6-Assign variable "seconds" the value of timer mod 60 with radix (base) 10.
seconds = parseInt(timer % 60, 10);

//7-Assign variable "minutes" to the value of "0" + minutes if minutes < 10, or minutes if not. This is accomplished with the ternary operator "?", which has syntax *condition ? exprT : exprF* 
minutes = minutes < 10 ? "0" + minutes : minutes;

//8-Assign variable "seconds" in the same way minutes are assigned, which adds a leading zero if the value is <10.
seconds = seconds < 10 ? "0" + seconds : seconds;

//9-Assign variable "output" to minutes concatenated with ":" concatenated with seconds
output = minutes + ":" + seconds;

//10-Decrement (lower) the value of timer by one first (since -- is in front), THEN check if that value is <0. If so, assign variable "timer" to the value of variable "duration", which was initially set by a parameter at the beginning of the setTimer function. This causes the timer to loop back to the initial duration once the timer passes zero. You could put different code here if you want a different result after the timer reaches zero.
if (--timer < 0) {
timer = duration;
//if you want to stop the function entirely when the function passes zero, uncomment the next line to end the function by returning nothing.
//return;
}

//11-Output the formatted timer to the console log. You could also use something like, "setText("id",output);" to set a UI element to the value of the timer.
console.log(output);

//12-End the function performed in setInterval. Also set the interval in which the function is repeated to 1000 ms (the second argument in the setInterval function).
}, 1000);

//13-End of function startTimer
}

//14-Start the timer by calling function "startTimer" with a 30 second duration
startTimer(30);
...